JPH0415728B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a polyester film for thermal transfer recording media carrying transfer ink used in thermal printers and the like that perform recording by thermal melt transfer or thermal sublimation transfer. Conventional technology and problems to be solved In recent years, thermal printers, thermal facsimile machines, etc. have used thermal transfer recording materials that are made by coating a thin polyester film with heat-melting transfer ink or heat-sublimation transfer ink. Clear and robust images are obtained. However, since this polyester film has a low thermal conductivity, it is necessary to reduce the thickness in order to obtain good thermal conductivity, but when it becomes an extremely thin film such as 3 to 6 μm, its mechanical strength decreases and it cannot be cut easily. Wrinkles occur and workability becomes extremely poor. In order to solve these problems, attempts have been made to increase the thermal conductivity of the base film by mixing fine particles with high thermal conductivity in polyester (JP-A-59-162090, JP-A-59- 174392). However, even in these methods, in order to increase the thermal conductivity of the base film, it is necessary to contain a large amount of a good thermal conductor, which has the drawback of deteriorating the mechanical properties of the film and causing coarse lumps. . In addition, as the content of the thermally good conductor increases, the cost increases, and at present there is no satisfactory method. There was a desire to find a way to obtain an effect. Means for Solving the Problems The present inventor has made extensive studies in order to reduce the content of a good thermal conductor in a polyester film, maintain the mechanical properties of the film, and obtain an excellent effect in terms of thermal conductivity. The inventors discovered that the problem could be solved by adjusting the physical properties of the polyester film within a certain range, and arrived at the present invention. That is, the present invention was measured by X-ray diffraction [100]
_The ratio of the peak value X ₁₀₀ of the plane to the peak value X ₁₁₀ of the [110] plane XI = X ₁₁₀ / The present invention relates to a polyester film for thermal transfer recording media characterized by containing fine particles of a good conductor. The polyester referred to in the present invention refers to aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, and naphthalene-2,6-dicarboxylic acid, or esters thereof, and diols such as ethylene glycol, diethylene glycol, tetramethylene glycol, and neopentyl glycol. It is a crystalline aromatic polyester that can be obtained by polycondensation of The polyester can be obtained by directly polycondensing aromatic dicarboxylic acid and glycol, or by polycondensing aromatic dicarboxylic acid dialkyl ester and glycol after transesterification, or by polycondensing diglycol ester of aromatic dicarboxylic acid. It can also be obtained by methods such as condensation. Representative examples of such polymers include polyethylene terephthalate, polyethylene-2,6 naphthalene dicarboxylate, polytetramethylene terephthalate, polytetramethylene-2,6
- Naphthalates, etc. This polymer may be a homopolymer that is not copolymerized, but as long as its properties are not deteriorated, 80 mol% or more of the repeating units are ethylene terephthalate or ethylene-2,6-naphthalate units, and 20 mol% of the repeating units are % or less of other components, or a mixed polyester obtained by adding and mixing other polymers to these polyesters. When adding or mixing other polymers to polyester, it is necessary to add or mix within a range that does not essentially change the properties of the polyester, and polyolefins, polyamides, polycarbonates, other polyesters, etc. must be added in a proportion of less than 15% by weight. Can be added. Further, the polyester may contain commonly used inert fine particles that act as a lubricant or the like, if necessary. The inert fine particles may be internal particles precipitated during polymerization, or may be inorganic or organic inert particles added from the outside. The thermally conductive fine particles of the present invention include metal oxides such as alumina particles, metals such as aluminum,
CaCO ₃ , inorganic compounds such as quartz glass, polymeric organic substances such as cellulose, etc., whose thermal conductivity at 273K is 10 W/m・deg or more, preferably 50 W/m・
There is no particular limitation as long as it is more than deg. The thermally conductive fine particles may be in either powder or fibrous form, but in the present invention, fibrous or rod-like particles are particularly preferred. Particle size is 0.001-5.0μm
The content is 0.1 to 15 wt%. The external particles and the thermally conductive particles may be added before polyester polymerization or during the polymerization reaction, or they may be kneaded in an extruder when pelletizing after polymerization, or they may be added during melt extrusion into a sheet. However, it may be dispersed in an extruder and extruded. In the present invention, the polyester film that is the base film has a ratio X _I of the peak value X ₁₀₀ of the [100] plane and the peak value X ₁₁₀ of the [110] plane measured by X-ray diffraction.
It is necessary that the value of =X ₁₁₀ /X ₁₀₀ be 0.09 or more. Here, a film with X _I of 0.09 or more can be obtained by suppressing the orientation of the benzene ring in the film plane. This can be accomplished, for example, by heat-setting a biaxially stretched film by a conventional method in one step at a high temperature of 245°C or higher, or by heat-setting it in two or more stages at a high temperature of 230°C or higher. A more preferable method is to stretch the film in a manner such that the orientation after stretching in the first axial direction is low during sequential biaxial stretching, and then to heat set it by stretching at 110°C to 150°C in a direction perpendicular to the first axial direction. . In this case, by lowering the orientation in the first axis direction, the degree of orientation of benzene rings on the film surface in the film after biaxial stretching is lowered,
It becomes possible to set X _I to 0.09 or more. This first
A specific method for achieving a birefringence index of 0.08 or less after axial stretching is 90°C or higher when stretching in one step.
It can be obtained by stretching at 3.5 times or less, but a preferred method is to use multiple steps to achieve a birefringence of 0.015 to 0.055 before final stretching, and then further stretching at 85°C in the same direction.
Obtained by final stage stretching of 1.1 to 1.9 times at a temperature of ~130°C. However, if the above-mentioned stretching recipe contains a large amount of fine particles of a good thermal conductor, the birefringence index may not be measured because the film becomes opaque. Therefore, the birefringence of a film containing a large amount of fine particles is substituted with the birefringence of a film that does not contain fine particles. A film that satisfies the above formula has a lower temperature when using the same type of thermally conductive fine particles than a film that does not fall within the range of the above formula.
Excellent print clarity can be obtained with a small amount of content. Although the reason is not clear, it is probably because the benzene rings in the polyester in the film of the present invention have a large inclination with respect to the plane of the film, and the mixed fine particles with good thermal conductivity may exist continuously in the thickness direction. It is thought that the overall thermal conductivity is improved. Next, the method for forming a polyester film of the present invention will be specifically explained. A polymer resin containing the necessary amounts of a matting agent, thermally conductive fine particles, and a slipping agent is dried by a conventional method, extruded through an extruder, and cooled and solidified on a rotating cooling drum to form an unstretched polyester. Form a sheet. At this time, electrostatic application cooling method etc.
It is also preferable to employ known cooling means. The unstretched film obtained in this way first has a birefringence Δn in the first axis direction, usually in the longitudinal direction.
0.080 or less, then stretched 2.5 to 4.5 times in a direction perpendicular to the uniaxial direction at a temperature of 90°C to 150°C, and heat set at 200°C to 250°C for 1 second to 10 minutes. In the present invention, it is most preferable to control X to 0.09 or less by setting Δn to 0.080 or less after first axial stretching, usually longitudinal stretching. It is also preferable to convert the first axial stretching into multistage stretching, or to apply super draw or near super draw stretching. Although the thickness of the film is not particularly limited, it is preferably 1μ to 50μ for this purpose. EXAMPLES The present invention will be explained in more detail below with reference to Examples, but it goes without saying that the present invention is not limited to these Examples. The evaluation method for each physical property of the film is shown below. (1) Birefringence Measure the retardation using a Carl Zeiss polarizing microscope, and calculate the birefringence (Δn) using the following formula.
I asked for Δn=R/d where R: Retardation d: Film thickness (2) 2θ=
The peak value of the (110) plane near 23° was read and the ratio (X _I ) was taken. The X-ray output was 30kV and 15mA. (3) Evaluation of thermal transfer material One side of a 6μ PET film was treated with silicone resin to prevent sticking, and the other side was coated with thermal transfer colored ink with a melting point of 65°C using a hot melt coater to use as a thermal transfer recording material. , typewriter EP-20 manufactured by Brother Industries, Ltd. and line printer P6 manufactured by Fuji Xerox Co., Ltd. were used for evaluation. Those with good evaluation results were rated ○, and those with poor evaluation results were rated ×. Δ is in between. (4) F ₅ − value A sample film with a width of 1/2 inch and a length of 50 mm between chucks was measured at 20°C and 65%RH using a Tensilon (UTN−) manufactured by Toyo Baldwin Co., Ltd.
The load at 5% elongation was divided by the initial cross-sectional area and expressed in kg/ ^mm2 . Examples 1 and 2 (Manufacture of polyester) 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol, and 0.11 parts of calcium acetate hydrate were placed in a reactor, heated to raise the temperature, and methanol was distilled off to perform a transesterification reaction. It took about 4 hours to reach 230°C, and the transesterification reaction was substantially completed. Triethyl phosphite is then added to this reaction mixture.
A solution obtained by uniformly dissolving 0.062 part of triethyl phosphate and 0.27 part of triethyl phosphate in ethylene glycol was added, and then 0.04 part of antimony trioxide was added, and the temperature was raised to 236°C over 10 minutes. From this point, the pressure in the system was gradually reduced, and 80 minutes after adding antimony trioxide, the temperature in the system was 265℃ and the pressure was 30mmHg, and after that, the temperature and pressure were gradually increased and the pressure was reduced to 285℃ and 1mmHg or less. . After 4 hours, the inside of the system was returned to normal pressure, and the polymer was discharged and made into chips to obtain polyester A. On the other hand, polyester B was obtained by kneading 10 wt % of alumina having an average particle size of 0.7 μm into the polyester A using an extruder and forming it into chips. These polyesters A and B were adjusted so that [η] was 0.63. (Method for producing polyester film) The above chips were mixed in a ratio of A:B = 9:1, dried in a conventional manner, extruded into a sheet at 285°C using an extruder, and rapidly cooled to form an amorphous sheet. The amorphous sheet was stretched 3.4 times at 105℃ to obtain Δn.
After setting it to 0.040, it was further stretched 1.25 times and 1.35 times at 105°C. The longitudinally stretched film thus obtained was then stretched in the transverse direction by a factor of 3.9 at 145°C using a tenter, and heat-set at 205°C to obtain a film of 6μ (Examples 1 and 2). The physical properties of the film are shown in Table 1. When this film was evaluated as a thermal transfer material, it showed good reproducibility with a thermal head and gave clear images. Comparative Examples 1 and 2 Using an amorphous sheet produced in the same manner as in the above example, the amorphous film was stretched 3.7 times in the longitudinal direction at 85°C, then stretched 3.9 times in the transverse direction at 100°C, and then stretched at 205°C.
A film of 6 μm (Comparative Example 1) was obtained by heat setting. The physical properties of the film are shown in Table 1. When this film was evaluated as a thermal transfer material, the reproducibility of the thermal head was poor, the lines were thin and broken, and some characters were missing, giving an unclear image. Therefore, in order to find out the amount of alumina that would give a good evaluation as a thermal transfer material, we investigated changing the blending ratio of polyester A and polyester B, and found that in this stretching method, the amount of alumina in the film is extremely large at 6 wt%. I realized that it was necessary. Example 3 Transverse stretching was carried out in the same manner as in Example 1, and the film was further stretched 1.15 times in the longitudinal direction, and then heat-set at 205°C. Comparative Example 3 Using an amorphous film prepared in the same manner as in Example 1, the amorphous film was stretched 3.95 times in the longitudinal direction at 85°C, then stretched 3.9 times in the transverse direction at 100°C, and then stretched at 205°C.
It was heat fixed.

[Table] Effects of the Invention As described above, the present invention has the structure described in the claims, that is, the X-ray diffraction measurement value of the polyester film, the value of X _I = X ₁₁₀ /X ₁₀₀ is 0.09 or more. As a result, it is possible to obtain a film that retains the mechanical properties of the polyester film itself and has excellent heat-sensitive transfer properties, and the film of the present invention is useful as a polyester film for heat-sensitive transfer recording media.

Claims (1)

[Claims] 1. Peak value of [100] plane measured by X-ray diffraction
Ratio of X ₁₀₀ to peak value X ₁₁₀ of [110] plane X _I = X ₁₁₀ /
1. A polyester film for thermal transfer recording media, characterized in that a base film having an X ₁₀₀ value of 0.09 or more contains fine particles of a good thermal conductor having a thermal conductivity higher than that of the base material.