JPH029686A - Biaxially oriented polyethylene terephthalate film for thermal transfer - Google Patents

Abstract

PURPOSE:To enhance the uniformity of a thermal transfer layer by using a polyester film, whose specific resistance at a melting time is set to a specific value, obtained using an electrostatic cooling method. CONSTITUTION:The specific resistance of polyethylene terephthalate at the time of melting must be 5X10<6>-5X10<8>OMEGA-cm. A metal component may be made soluble in polyethylene terephthalate in order to reduce specific resistance and, for the sake of this, for example, a means for adding a relatively small amount of a phosphorus compound to a metal element used as an transesterification catalyst or a metal element added during or after reaction is pref. In order to increase specific resistance, the amount of the metal element dissolved in polyethylene terephthalate may be reduced and, concretely, the addition amount of a metal compound soluble in a reaction system may be reduced or the greater part of the metal compound may be precipitated as a metal salt insoluble in polyethylene terephthalate.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a thermal transfer recording film,
More specifically, the present invention relates to a base film for thermal transfer that improves the uniformity of the transfer layer and is suitable for high-speed printing.

[Problems to be solved by conventional technology and invention]

Although various recording methods have been known in the past, a thermal transfer method using a thermal recording device such as a thermal printer is widely used because of its excellent operability and maintainability. The base film for this printer transfer agent has a high melting point,
Polyester films, particularly λ-axis oriented films of polyethylene terephthalate, are used because they have excellent heat resistance, chemical resistance and mechanical properties, and are relatively inexpensive.

However, in recent years, high-speed transfer has progressed, and in addition to the conventional required properties such as film runnability and staking resistance, uniformity of heat-sensitive transfer materials, particularly uniformity of the ink layer, has become required. That is, in order to enable a thermal transfer material to be used for a long time and to achieve miniaturization, it is desirable to make the base film thinner, and especially to make the ink layer thinner. However, in this case, the thickness of the ink layer significantly affects printing performance, so the ink layer must have a thickness as uniform as possible. Furthermore, if the thickness of the thermal transfer material is uneven, the contact with the thermal head will not be uniform, resulting in head contamination and wear.

However, this point has not always been fully achieved with conventionally used polyester films.

[Means for solving problems]

As a result of intensive studies in view of the above problems, the inventor of the present invention discovered that a thermal transfer material made of polyethylene terephthalate having certain electrical characteristics has excellent uniformity and is suitable for high-speed printing. This led to the invention.

That is, the gist of the present invention is a polyester film obtained using the electrostatic cooling method, which has a specific resistance when melted! ;
The present invention relates to a biaxially oriented polyethylene terephthalate film for thermal transfer, characterized in that the film has a resistance of X/0' to jX/08Ω-1.

The present invention will be explained in detail below.

Polyethylene terephthalate as used in the present invention has ethylene terephthalate units as the main repeating structural unit, but other units such as phthalate, isophthalic acid, etc. A
- Naphthalene dicarboxylic acid and its isomers, adipic acid, sebacic acid, oxycarboxylic acid, diethylene glycol, propylene glycol, butanediol, /, 9-
It may contain units such as cyclohexane dimetatool and neopentyl glycol. In any case, the term "polyethylene terephthalate" as used in the present invention refers to a polyester having ethylene terephthalate units in mol% or more of repeating structural units.

In the present invention, a biaxially oriented film is obtained using such polyethylene terephthalate as a raw material, and the following method is adopted for this purpose.

That is, the sheet is cooled to 1Io to 70°C at a temperature usually in the range of 2gθ to 310°C, and then the sheet-like material is multiplied by at least an area magnification in the longitudinal and transverse directions. The film of the present invention can be obtained by stretching the biaxially oriented film to such an extent that the film becomes biaxially oriented, and then heat-treating the film at a temperature in the range of 0°C to 2'10°C.

In the present invention, a biaxially oriented polyethylene terephthalate film is obtained in this way, and in the present invention, the specific resistance of such polyethylene terephthalate when melted is &gt;
X/06~j The flatness of such biaxially stretched films largely depends on the uniformity of the amorphous sheet, especially when the film thickness is 30 mm.
This phenomenon becomes noticeable in the region of μm or less. That is, if polyethylene terephthalate has a specific resistance when melted of Ω/0' to &X/0'', a uniform amorphous sheet can be obtained by the electrostatic cooling method.

The flatness of the film of the present invention may vary somewhat depending on the conditions of electrostatic application. Therefore, the specific resistance value when melted is 3;
A film for thermal transfer is a film that is within the range of & Particularly preferred as

Specific resistance when melted! ; X / 0"Ω - beyond the opening, thickness unevenness often occurs even if the electrostatic application conditions are maintained appropriately.
．． It exceeds 1%5, and on the contrary, the resistivity becomes &X/0
If it is less than 60-α, the thermal stability of the polyester is poor and degraded products are often generated. A more preferable range of the specific resistance is 7X/06~/X/
08Ω-α.

In addition, in order to adjust the specific resistance during melting to a desired value, the following method may be adopted for K.

That is, in order to reduce the specific resistance, it is sufficient to solubilize the metal component in polyethylene terephthalate, and for this purpose, for example, the metal element used as the transesterification reaction medium or the transesterification reaction or esterification as necessary After the reaction, it is preferable to add a comparatively small amount of phosphorus compound to the added metal element, for example, an equivalent molar amount or less.

On the other hand, in order to increase the resistivity, it is sufficient to reduce the amount of metal elements dissolved in polyethylene terephthalate. Specifically, it is necessary to reduce the amount of metal compounds that are soluble in the reaction system, or to reduce the amount of metal compounds that are soluble in the reaction system. Even if a considerable amount of
For example, it may be precipitated as a carboxylate, phosphate, or phosphite. More specifically, this can be achieved, for example, by reacting a phosphorus compound in an equivalent molar amount or more to a metal element such as calcium or manganese used as a transesterification catalyst.

In addition, since the specific resistance value at the time of melting does not change by film formation or remelting, even if the film of the present invention is recycled and made into a film, a uniform film can be obtained in the same way.

Further, as a secondary effect of the present invention, improvement in productivity during film formation can be mentioned. That is, when obtaining the film of the present invention, the cooling effect during production of the amorphous sheet is excellent, making it possible to increase the speed of the rotating cooling drum and furthermore, the production line, thereby achieving cost reduction.

In the film of the present invention, it is preferable that inert fine particles be blended with the polyester to appropriately roughen the surface of the film in order to improve the runnability and sticking resistance of the film.

Examples of these inert particles include kaolin, talc,
Magnesium carbonate, calcium carbonate, barium carbonate, calcium sulfate, barium sulfate, lithium phosphate, calcium phosphate, magnesium phosphate, aluminum oxide,
Examples include, but are not limited to, seven or more metal compounds selected from silicon oxide, titanium oxide, etc., carbon black, and the like.

The shape of this inert compound may be spherical, blocky or flat, and there are no particular limitations on its hardness, specific gravity, color, etc. The average particle size of the inert compound is usually 0.05 mm in diameter. /~10μ, preferably 0.3~3
Selected from the range μ. In addition, the blending amount for the film is o, O7 to io weight %, preferably 0.0s to io!
% by weight, more preferably 0. / to 3 times i%.

In the present invention, when the surface roughness of the film developed by the presence of such fine particles satisfies certain requirements, more preferable results as a base film for thermal transfer can be obtained.

That is, when the center line average roughness of the film is Ra (μm) and the maximum protrusion height is Rt (μm), Ra is 0.02 to
The range of 7.0 μm is preferable, and at the same time Rt/Ra is 5 to 5.
It is preferably in the range of 20. If Ra is less than 0.02, the running properties and anti-staking properties of the film will be insufficient, and if this value exceeds 0.0, printing performance will deteriorate. Furthermore, Rt/Ra is a measure of the uniformity of the protrusion height, but if this value is less than 5, unevenness between the film and the base material is likely to occur; If it exceeds 5VC, thickening of ink, old paper and thermal transfer material will occur.

In the present invention, the type of heat-sensitive transfer layer formed on the base film is not limited, and either a non-reactive type or a reactive type can be used. Non-reactive types include, for example, transfer layers made of hot-melt ink or sublimable dyes, and reactive types include, for example, a combination of leuco dye and color developer. I can do it.

In addition, in the present invention, the thickness of the λ-axis stretched film is 0.
．． The thickness is 5 to 30 μm, preferably 7 to 70 μm, and more preferably 6 to 6 μm.

〔Example〕

The present invention will be explained in more detail below using Examples and Comparative Examples, but the present invention is not limited to the following Examples unless it exceeds the gist thereof.

In the examples and comparative examples, "parts" indicate "parts by weight."

Further, the measurement method used in the present invention is shown below.

(1) Resistivity during melting British Applied Physics (
Br1t, J, Appl, Phys, ) No. 17
Volume, 1/q9~/l! The method is described on page R (Zoro 6). However, in this case, the melting temperature of the polymer is 29 parts Celsius, and the value immediately after applying a direct current /, o00 V is taken as the specific resistance at the time of melting.

(2) Planarity of the film The film thickness is measured at 10 points every 1000 m in the longitudinal direction of the film, 10 points every 10 CrrL in the lateral direction, a total of 100 points.

The thickness of the film is measured using a micrometer manufactured by Anritsu Denshi, and the thickness is measured by stacking 10 films around the relevant location and converting the thickness to 1 film.

The maximum value of all measured values is Xmax, the minimum value is Xm
1n, when the arithmetic mean value is also taken as Xmax, -Xm1n
.

Let X be F′″4′) thickness 4 unevenness.

(3) Center line average roughness (Ra) It was determined as follows using a surface roughness meter (SE-, 7FK) manufactured by Koita Research Institute. The tip radius of the stylus is 24 m, and the load is 30 m9. A part of reference length L (2, & shoulder π) is extracted from the film cross-sectional curve in the direction of its center line, and the roughness curve y = When expressed as f (x), the value given by the following formula is expressed in μm.

Ra = 'f''If(x)IdX The cut-off value is 10 μm, and Ra is the left point in the vertical direction,
Measurements were made at 10 points in total, including the left point in the horizontal direction, and the average value was calculated.

(4) Maximum protrusion height (Rt) This is expressed as the difference between the maximum and minimum values of the cross-sectional curve obtained when measuring the centerline average roughness. Measurements were made at IO points in the same way as Ra, and the average value was taken as Rt.

(5) Film running properties during printing First, transfer ink was applied to the base film. That is,
On one side of the film, a heat-melting color material layer consisting of 3 parts of paraffin wax, 3 parts of carnauba wax, 13 parts of low molecular weight polyethylene, and 2 parts of carbon bran was applied so that the dry film thickness was on average 1 μm. It was painted on.

Note that the thickness is on the side opposite to the coloring material layer. A 34 m silicon-based heat-resistant protective layer was provided.

Next, a facsimile telecopier made by Fuji Xerox.
Using a 41-part machine, the running conditions of the heat-sensitive transfer film obtained in the above manner were evaluated and divided into the following three stages.

○...The feeding condition is good and there is no gap at all.

△...The ribbon may be slightly wrinkled.

X: The ribbon is wrinkled and the feeding condition is often poor.

(6) Printability Printability was evaluated using the same evaluation machine and film as in the evaluation of film runnability for printability, and was divided into the following three stages.

◎・・・・・・Excellent condition with no shading or bleeding ○・・・
・・・Good condition with almost no shading or bleeding △・・・・・・
Slight uneven shading and bleeding are observed.

X: Unevenness in shading or blurring is clear.

Example 1 (Production of polyethylene terephthalate) 700 parts of dimethyl terephthalate, 60 parts of ethylene glycol, and 0.7 parts of calcium acetate hydrate were placed in a reactor and a transesterification reaction was carried out. then ethyl acid phospha)
After adding 0.0.5-part of calcium carbonate with an average particle size of 1.78 m and 0.0 part of antimony trioxide
Part If was added, and a polycondensation reaction was carried out in a conventional manner. The reaction was stopped one hour after the start of the reaction, and the limiting viscosity reached 0.
A2 polyethylene terephthalate was obtained.

The specific resistance of the obtained polyester when melted is koX/θ7Ω
-α. Further, the added particles were uniformly dispersed.

(Manufacture of polyethylene terephthalate film) Next, the obtained polyester was added to 29! ;'C, it was extruded into a sheet from an extruder and an amorphous sheet was obtained using an electrostatic cooling method. That is, as a positive electrode, the diameter is 0. A tungsten wire made by Og was stretched on the upper surface of a rotating cooling drum in a direction perpendicular to the flow of the sheet, and a DC voltage of 9 KV was applied thereto.

Next, the obtained amorphous sheet was stretched 3.5 times in the longitudinal direction and 3.5 times in the transverse direction, and heat-treated at 220°C to a thickness of 3.3 times.
A micrometer biaxially stretched polyethylene terephthalate film was obtained.

(Evaluation as a heat-sensitive transfer material) Transfer ink and a heat-resistant protective layer were coated on the thus obtained polyethylene terephthalate film, and evaluation as a heat-sensitive transfer material was performed.

Examples λ to q Films were obtained in the same manner as in Example 1, except that the specific resistance during melting and the average particle size and amount of particles contained were changed, and then evaluated as thermal transfer materials.

Comparative Example 1 An amorphous sheet was obtained using the same polyethylene terephthalate as in Example 1 and using an air knife instead of the electrostatic cooling method. Next, a biaxially stretched film was obtained in the same manner as in Example/1, and evaluated as a heat-sensitive transfer material.

Comparative Example: In Example 1, the specific resistance qx of polyester when melted
A polyethylene terephthalate film was obtained in the same manner as in Example, except that iθ8 was changed, and then evaluated as a thermal transfer material in the same manner as in Example.

The results obtained above are summarized in Table 7.

〔Effect of the invention〕

According to the film of the present invention, the uniformity of the heat-sensitive transfer layer is improved, and a base film for heat-sensitive transfer suitable for high-speed printing can be obtained, and its industrial value is high.

Claims (1)

[Claims] (1) A polyester film obtained using an electrostatic application cooling method, which has a specific resistance when melted of 5×10^6 to 5×
2 for thermal transfer characterized by 10^8 Ω-cm
Axially oriented polyethylene terephthalate film.