JP3010635B2 - Polyester film for thermal transfer - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a thermal transfer film, and more particularly, to a thermal transfer polyester film excellent in printing characteristics and slitting properties.

[Problems to be solved by conventional technology and invention]

Conventionally, various recording methods are known,
A thermal transfer recording system using a thermal recording device such as a thermal printer is widely used because of its excellent operability and maintainability. As a base film of the transfer material for the printer, a biaxially oriented film of polyester, especially polyethylene terephthalate, has been used because of its high melting point, heat resistance, chemical resistance, and mechanical properties. Was.

In particular, since the mechanical properties of the polyester film are directly related to the printing properties, various studies have been made so far. For example, British Patent No. 1,003,704 discloses the use of a film oriented strongly in the longitudinal direction.
-77412 discloses F5 value in the longitudinal direction (stress at 5% elongation)
Is suppressed to 10 kg / mm ² or less, and an example of a film oriented more strongly in the horizontal direction is disclosed in Japanese Patent Application Laid-Open No. Sho 60-217194.Examples of a film in which mechanical strength is balanced in both the vertical and horizontal directions are shown. ing.

According to the inventor's knowledge, the mechanical strength is preferably substantially balanced in both the vertical and horizontal directions, but in order to cope with recent high speed and precision, a conventionally known film is used. There is a need for a film that is not always sufficient and has more appropriate properties.

That is, the base film for thermal transfer is usually coated with a heat-meltable or sublimable ink layer on one side, and after applying a heat-resistant protective layer on the other side, slit and then rolled up to form a strip. In this case, if the slitting property of the base film is poor, the coating layer is stretched or the edges are raised, and as a result, the ink layer applied to the film is transferred to the opposite surface (running surface), It causes obstacles such as contamination of the guide pins and thermal head of the traveling system.

Conventionally, sufficient consideration has not been given to such a problem, and an appropriate base film has not been known.

In addition, if the running property of the base film is poor, smooth conveyance of the ribbon is hindered and wrinkles are easily formed, and if the degree is significant, the running stops, so the base film has the following basic physical properties. Moderate traveling performance is required.

[Means for solving the problem]

The present inventor has conducted intensive studies in view of the above problems, and as a result, has found that a film having a certain value with respect to certain physical properties overcomes the above problems and is useful as a thermal transfer film, and has completed the present invention. Was.

That is, the gist of the present invention is that the F5 value in the vertical and horizontal directions is 1
0.5～17.0Kg / mm ^2, wherein the absolute value of birefringence is from 0.022 to 0.080, the refractive index in the thickness direction is from 1.487 to 1.496, and microprojection density of the film surface is within the range of 100 to 500 pieces / mm It exists in the polyester film for thermal transfer.

 Hereinafter, the present invention will be described in detail.

The polyester in the present invention is terephthalic acid, 2,6
-An aromatic dicarboxylic acid such as naphthalenedicarboxylic acid or an ester thereof, and a polyester obtained by using ethylene glycol as a main starting material, but may contain other components. In this case, as the dicarboxylic acid component, terephthalic acid, phthalic acid, isophthalic acid, 2,6-
Naphthalenedicarboxylic acid and its isomers, adipic acid,
One or more of oxycarboxylic acids such as sebacic acid and p-oxyethoxybenzoic acid can be used. As the glycol component, diethylene glycol, propylene glycol, butanediol, 1,4-
One or more of cyclohexane dimethanol, neopentyl glycol and the like can be used. In any case, the polyester of the present invention is a repeating structural unit.
80% by mole or more refers to a polyester having an ethylene terephthalate unit or an ethylene-2,6-naphthalene unit.

Further, the polyester film of the present invention is a polyester film oriented in both the vertical and horizontal directions using such a polyester as a starting material, and its F5 value is in the range of 10.5-17.0 kg / mm ² in both the vertical and horizontal directions. There must be. When this value is less than 10.5, the film is easily stretched and elastic recovery is difficult, so that plastic deformation occurs and printing is performed thickly, resulting in poor sharpness. On the other hand, if this value exceeds 17.0, the thermal head shrinks greatly during printing, and clear printing becomes impossible.

The F5 value is preferably selected from the range of 10.5-15.0, more preferably 10.8-14.0, both in the vertical and horizontal directions.

The ratio of the F5 value in the vertical direction to the F5 value in the horizontal direction is in the range of 0.7 to 1.5, preferably 0.9 to 1.4.

In the film of the present invention, the absolute value of the birefringence, i.e. the absolute value of the difference between the longitudinal refractive index n _MD and transverse direction refractive index n _TD must be 0.022 to 0.080. This value preferably ranges from 0.023 to 0.040, more preferably from 0.025 to 0.035.

By the way, the refractive index, which represents the orientation of the molecular chains of the film, and the F5 value, which represents mechanical strength, have a macroscopic correlation, but when viewed in detail, they do not always correspond uniquely. do not do. That is, for example, a film having a larger F5 value in the vertical direction can be obtained even when the refractive index in the horizontal direction is larger depending on the film forming conditions in the sequential stretching.
In this phenomenon, the refractive index reflects the state of the amorphous and crystalline regions as a whole, while the mechanical strength is strongly affected by the orientation state of the amorphous region, particularly the typological concept. It is believed that.

In any case, in the present invention, the absolute value of birefringence needs to be in a relatively large range as described above,
This indicates that the molecules are more strongly oriented vertically or horizontally as a whole. And, by such a feature, the film of the present invention can obtain excellent slitting properties, and as a result, can perform precise printing without contaminating the system even when the thermal transfer agent is run at high speed. .

In the present invention, the refractive index in the thickness direction of the film needs to be in the range of 1.487 to 1.496, preferably 1.489 to 1.494. If this value is less than 1.487, the adhesion between the film and the ink layer often deteriorates, and if this value exceeds 1.496, the slitting property of the film deteriorates, and finally contamination of the process occurs.

The film of the present invention further improves the slitting property of the film by keeping the density of fine protrusions on the film surface in a specific range.

The improvement of the slit property is based on the following findings of the present inventors.

That is, the present inventor has found that if a very large number of different components are finely dispersed in the film, the slit property can be improved without impairing other characteristics. It has been found that the degree of the improvement has a very good correlation with the density of the fine projections on the film surface which is developed by the presence of the foreign component.

The reason why the above phenomenon occurs is not clear, but it is considered that the infinite number of finely dispersed components in the film moderately disturbs the polyester molecule and crystal structure and improves the slitting property.

The density of fine projections referred to in the present invention can be measured by a stylus type surface roughness meter. At this time, the radius of the stylus is 2 μm, the stylus pressure is 30 mg, the cutoff value is 0.08 mm, the magnification in the vertical direction is 100,000, the magnification in the horizontal direction is 500, and the film surface is measured by 1 mm. Fine protrusions having a difference of 1.0 mm or more between the level of the peak on the chart of the obtained roughness curve and the level of the valley on the left side thereof are defined.

The fine projection density of the film surface of the present invention is 100 to 500 / m
must be m. If this value is less than 100, the improvement of the slit property is insufficient, and if it exceeds 500, the overlapping of the projections increases and coarse projections are formed, resulting in poor printing characteristics.

And the above-mentioned fine projection can be expressed by several methods. For example, 0.1 to polyester film
It can also be obtained by blending organic or inorganic fine particles of about 5 μm, or alternatively, by blending another thermoplastic resin with polyester and then forming a film.

The presence of the fine projections can also contribute to the improvement of the running property at the same time, which is also advantageous from this point.

It is already known that the improvement of the running property is achieved by making the film surface somewhat rough, that is, about 0.02 to 1 μm, preferably 0.1 to 0.4 μm in center line average roughness, Therefore, when the main object is to improve running properties, it is better to select the blended particles in consideration of this point.

As a method for producing a polyester film in the present invention, for example, the following method can be employed.

That is, after the polyester is melt-extruded into a sheet at 270 to 310 ° C., cooled and solidified at 40 to 80 ° C. to form an amorphous sheet, and then vertically and horizontally, biaxially or simultaneously stretched,
Then, a method such as heat treatment at 160 to 240 ° C. is used. Of course, if necessary, a method of stretching in the vertical or horizontal direction after stretching biaxially may be adopted. In the present invention, it is necessary to select from these film forming conditions such that a film having the physical properties of the present invention can be obtained. Particularly preferred embodiments are as follows.

The unstretched sheet is first stretched in one or more stages at about 90 to 100 ° C. so that the total magnification becomes 3.7 to 5.2 times.
Then, it is stretched 3.5 to 4.0 times in the transverse direction at about 90 to 110 ° C.
In this case, the stretching ratio is smaller than that in the longitudinal direction.

Then, while adding 0 to 10% lateral relaxation in the tenter
Heat treatment at 210-235 ° C.

By the above operation, having an appropriate refractive index in the thickness direction,
The refractive index in the vertical direction is about 1.665 to 1.680, and the refractive index in the horizontal direction is about
A more strongly blended film in the machine direction can be obtained in the range of 1.640 to 1.650.

The unstretched sheet is vertically stretched at a total magnification of about 90-100 ° C.
It is stretched in one step or multiple steps so as to be 3.0 to 4.0 times. Then, it is stretched 3.7 to 5.0 times in the transverse direction at about 90 to 110 ° C. In this case, the stretching ratio is made larger than that in the longitudinal direction.

Then, while adding 0 to 10% lateral relaxation in the tenter
Heat treatment at 210-235 ° C.

By such an operation, it has a suitable refractive index in the thickness direction, the refractive index in the vertical direction is about 1.640 to 1.655, the refractive index in the horizontal direction is in the range of about 1.665 to 1.680, and more strongly oriented in the horizontal direction. A film can be obtained.

The type of the heat-sensitive transfer layer formed on the base film of the present invention is not limited, and a non-reaction type or a reaction type may be used arbitrarily. Examples of the non-reactive type include a transfer layer composed of a hot-melt ink or a sublimable dye, and examples of the reactive type include a combination of a leuco dye and a developer. Can be.

〔Example〕

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples as long as the gist of the present invention is not exceeded.

 The measuring method used in the present invention is as follows.

(1) F5 value Intesco Corporation tensile tester Intesco Model 2001
Using a mold, a sample film having a length of 50 mm and a width of 15 mm was pulled at a speed of 50 mm / min in a room controlled at a temperature of 23 ° C. and a humidity of 50% RH, and the strength at 5% elongation was defined as F5 value.

(2) Refractive index A longitudinal refractive index n _MD , a lateral refractive index n _TD and a thickness direction refractive index n α of the film were measured using an Atago Optical refractometer.

 The birefringence Δn in the present invention is obtained by the following equation.

Δn = | n _MD− n _TD | (3) Film running property during printing First, a transfer ink was applied to a base film. That is, a heat-fusible coloring material layer composed of 35 parts of paraffin wax, 30 parts of carnauba wax, 15 parts of low-molecular-weight polyethylene, and 12 parts of carbon black was dried on one side of the film to a dry thickness of 2.5 μm.
m. Note that a silicon-based heat-resistant protective layer having a thickness of 0.5 μm was provided on the surface opposite to the color material layer.

Next, a facsimile telecopier made by Fuji Xerox
Using a 245 type machine, the running state of the thermal transfer film obtained as described above was evaluated and divided into the following three stages.

 …: The feeding state is good and there is no problem at all.

 Δ: The ribbon may be slightly wrinkled.

×: The ribbon is wrinkled or the feeding state is often poor.

(4) Printability The same evaluation machine as used for the evaluation of film runnability during printing,
The printability was evaluated using the film and divided into the following three stages.

 …: Good without shading or bleeding.

 Δ: slight shading and blurring are observed.

 X: Shading or blurring is clear.

(5) Slit property of film The quality of the slit property was evaluated by the degree of ink transferability. That is, a ribbon formed into a roll shape by slitting to a width of 10 mm was unwound and run over a length of 200 m, and dirt on a guide pin in contact with the heat-resistant protective layer was observed and evaluated in the following three stages.

 …: Adhesion of ink is hardly observed.

 Δ: Some adhesion of ink was observed.

 ×: considerable adhesion of ink is observed.

Example 1 In a polyester production process, after transesterification, 1.2 parts of silicon dioxide having an average particle size of 1.2 μm was added, and a polycondensation reaction was carried out by a conventional method to obtain a polyester terephthalate having an intrinsic viscosity of 0.63.

Next, the obtained polyester was dried, melted at 290 ° C., extruded from a T-die, and rapidly cooled to obtain an unstretched sheet. Subsequently, 3.1 times at 100 ° C in the vertical direction, and 1.1 times at 99 ° C.
After stretching twice, it was stretched 4.1 times in the transverse direction at 105 ° C.

Further, heat treatment was performed at 225 ° C. to obtain a biaxially oriented polyethylene terephthalate film having a thickness of 5 μm.

Apply the transfer ink and heat-resistant protective layer on the above film,
Evaluation as a thermal transfer agent was performed. The results obtained are shown in Table 1 together with those of the other Examples and Comparative Examples.

Example 2 A biaxially stretched film was obtained in the same manner as in Example 1, except that the method of stretching the unstretched sheet was changed.

That is, 3.7 times vertically at 87 ° C, then 95 times horizontally.
The film was stretched 4.6 times at ℃ and heat-treated at 225 ° C.

Next, in the same manner as in Example 1 using the obtained film,
Evaluation as a thermal transfer agent was performed.

Example 3 In Example 1, the stretching conditions were as follows.
And then stretched 1.8 times at 80 ° C and then at 105 ° C in the transverse direction.
A film was obtained in the same manner as in Example 1 except that the conditions for stretching 3.9 times were adopted, and the same evaluation as in Example 1 was performed.

Comparative Example 1 In the production of the film of Example 1, the stretching in the machine direction was 87
A film was obtained in the same manner as in Example 1 except that the stretching in the transverse direction was changed to 3.8 times at 92 ° C and the stretching in the transverse direction was changed to 4.0 times, and the same evaluation as in Example 1 was performed.

Comparative Example 2 A film was obtained in the same manner as in Example 1 except that the amount of silicon dioxide was changed to 0.03 part.
The same evaluation was performed.

Comparative Examples 3 and 4 The film manufacturing method was changed in Example 1 and
And the same evaluations as in Example 1 were performed.

As is clear from the results in Table 1, the films of Examples 1 to 3 satisfying the requirements of the present invention have excellent properties as a thermal transfer agent, whereas the films of Comparative Example 1 having a small birefringence are Poor slitting properties and poor printing characteristics.

Comparative Example 2 is an example in which the fine projection density is small,
Slit properties and running properties are also insufficient.

Comparative Example 3 shows that the F5 value in the vertical direction is too large, inevitably increases the heat shrinkage during printing and deteriorates the printability, and Comparative Example 4 shows that the F-5 value is too small. In addition to the fact that the film is easily stretched and the printed portion is deformed,
As in the case of Comparative Example 1, the problem caused by the small birefringence is shown.

[Effects of the Invention] The polyester film for thermal transfer of the present invention can maintain the printing characteristics at a high level and can also satisfy the slit property, which has been difficult to improve conventionally, and has great industrial value.

Claims (1)

(57) [Claims] (1) a vertical and horizontal F5 value of 10.5-17.0 kg / mm ² ,
The absolute value of birefringence is 0.022 to 0.080, and the refractive index in the thickness direction is 1.
487 to 1.496, and the density of fine protrusions on the film surface is 100 to 5
A polyester film for thermal transfer, characterized in the range of 00 pieces / mm.