JPH0678022B2 - Transfer material for thermal transfer printer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a transfer material for a thermal transfer printer, and more specifically, it has excellent dimensional stability, durability, sticking resistance, and printability used in a thermal transfer printer. Ink transfer material.

[Prior art] Thanks to the widely used biaxially oriented polyester film as the base of the transfer material for transfer printer, it has excellent properties such as high crystallinity, high melting point, heat resistance, chemical resistance, strength and elastic modulus. Has been done.

However, in order to shorten the input time to the heating head in order to increase the recording speed, it is necessary to accelerate the heat transfer, and it is necessary to make the heat-sensitive recording film thin or increase the input power. However, the transfer material using the conventional biaxially oriented polyester film has the following problems.

That is, if the base film is thinned in order to improve heat conduction, the strength is insufficient and the film is elongated during transfer, so that good transfer cannot be obtained.

Therefore, in order to maintain the vertical strength, the Young's modulus in the vertical direction is 700 kg /
When using a toughened polyester film exceeding mm ² , the thermal dimensional stability is poor and the thermal shrinkage during transfer is too large.
Again, good transfer cannot be obtained.

Furthermore, during printing, the heat transfer recording film is heated by a heating head to a temperature of 250 to 300 ° C. or higher, which causes the base film to partially fuse to the head, preventing the transfer material from being fed. To be This phenomenon is called a stick, which not only makes the recording clear but also causes troubles such as defective running of the thermal transfer film. This phenomenon is more likely to occur as the base film is flat, and if the surface of the base film is made too rough, the image quality lacks clarity.
Ink may not be transferred uniformly, resulting in a reduction in resolution. On the other hand, there is also a method of providing a heat-resistant protective layer such as thermoplastic resin, but not only is the process of manufacturing the transfer material complicated and costly, but if the heat-resistant protective layer is thick enough to prevent sticking, printing It is not a sufficient solution because of the poor resolution.

[Object of the Invention] An object of the present invention is to provide a transfer material for a thermal transfer printer, which eliminates the above-mentioned drawbacks, has excellent dimensional stability and durability, is suitable for speeding up printing, and has clear printing. is there.

According to the present invention, there is provided a transfer material for a thermal transfer printer having a thermal transferable colored layer which is melted by heating on one side of the biaxially oriented polyester film. The film has (a) a thickness in the range of 2 to 10 μm, and (b) the distribution curve showing the relationship between the number of protrusions (y: number / mm ² ) on the film surface and the protrusion height (x: μm). The curve above the maximum of the distribution curve is expressed by the formula: log ₁₀ y = -2.4x
Number of protrusions (Ymax: number / mm ² ) and protrusion height (Xmax: μm) when crossing at least once with +3.7 and the maximum value of the distribution curve
Relationship formula satisfies the log ₁₀ Ymax> -2.4Xmax + 3.7, further projection height (x) 0.8 [mu] m of the projections is in the range of 40 to 200 pieces / mm ^2, (c) vertical Young's modulus Is in the range of 550 to 700 kg / mm ² , (d) the heat shrinkage in the longitudinal direction when heat-treated at 150 ° C for 30 minutes is 3% or less, and (e) the density is 1.390 g / cm ³ or less. This is achieved by a transfer material for a thermal transfer printer, which is characterized by having the following characteristics.

The polyester in the present invention is a polyester having a main repeating unit consisting of ethylene terephthalate, and other components such as dicarboxylic acids, glycoliis, oxycarboxylic acids and the like which can be copolymerized therewith.
It does not matter even if it is less than 20 mol% copolymerized. These polyester films can be produced by a method known per se.

The biaxially oriented polyester film of the present invention has a large number of fine projections on the surface of the film. These large numbers of fine protrusions originate from the large number of substantially inert solid fine particles contained in the polyester.

A polyester film containing a large number of inert solid fine particles is usually used in a reaction for forming a polyester, for example, at any time during a transesterification reaction or a polycondensation reaction in the case of a transesterification method, or a direct polymerization method. Can be prepared by adding inert solid fine particles (preferably as a slurry in glycol) to the reaction system at any time. Preferably, the inert solid fine particles are added to the reaction system at the initial stage of the polycondensation reaction, for example, until the intrinsic viscosity reaches about 0.3.

In the present invention, the inert solid fine particles are preferably silicon dioxide (including hydrates, diatomaceous earth, silica sand, quartz, etc.); alumina; silicates containing 30% by weight or more of SiO ₂ ( For example, amorphous or crystalline clay minerals, aluminosilicates (including calcined products and hydrates), asbestos,
Zircon, fly ash, etc.); Mg, Zn, Zr, and Ti oxides; Ca and Ba sulfates; Li, Na, and Ca phosphates (including monohydrogen and dihydrogen salts); Li , Na, and K benzoates; Ca, Ba, Zn, and Mn terephthalates; M
titanates of g, Ca, Ba, Zn, Cd, Pb, Sr, Mn, Fe, Co, and Ni;
Examples include Ba, and Pd chromates; carbon (eg, carbon black, graphite, etc.); glass (eg, glass powder, glass beads, etc.); Ca, and Mg carbonates; fluorspar; ZnS, etc. More preferably, anhydrous silicic acid, hydrous silicic acid, aluminum oxide, aluminum silicate (including calcined products, hydrates, etc.), 1 lithium phosphate, 3 thylium phosphate, sodium phosphate, calcium phosphate, barium sulfate, titanium oxide, Examples include lithium benzoate, double salts of these compounds (including hydrates), glass powder, clay (including kaolin, bentonite, clay, etc.), talc, diatomaceous earth, calcium carbonate and the like. Particularly preferably,
Examples thereof include silicon dioxide, titanium oxide, calcium carbonate, and kaolin, either alone or in a mixture.

The average particle size of these inert solid fine particles is 0.05 to 10μ.
m, preferably 0.1 to 5 μm, and the amount added is preferably 0.03 to 5% by weight.

The biaxially oriented polyester film of the present invention has a thickness of 2-10.
It needs to be μm. If the thickness is larger than the above range, the resolution becomes poor and the heat transfer takes time, which is not suitable for high speed printing. On the other hand, if the thickness is less than the above range, the strength is low and the processability in the transfer material manufacturing process is poor, which is not preferable.

The biaxially oriented polyester film of the present invention further has a distribution curve showing the relationship between the number of protrusions (y: number / mm ² ) and the height of the protrusion (x: μm) as a film surface characteristic. The curve of the portion higher than the maximum value (the portion where the protrusion height is large) intersects with the formula: log ₁₀ Y> −2.4x + 3.7 at least once and the number of protrusions (Yma
x: number / mm ² ) and the height of the protrusion (Xmax: μm) are expressed by the formula: log
₁₀ Ymax> −2.4Xmax + 3.7 must be satisfied, and further, the projection height (x) of 0.8 μm must be 40 pieces / mm ² or more and 200 pieces / mm ² or less.

When the relationship between the number of protrusions (Ymax: pieces / mm ² ) and the height of the protrusions (Xmax: μm) does not satisfy the formula: log ₁₀ Ymax> −2.4Xmax + 3.7, 40 protrusions with a protrusion height of 0.8 μm If it is less than / mm ² , the film surface is too flat, resulting in poor slipperiness, wrinkling of the film, troubles during processing, and sticking on the heating head. Also, the number of protrusions (y: number / mm ² ) and protrusion height (x:
In the distribution curve representing the relationship between the [mu] m), the curve of the maximum higher value portion of the protrusion distribution curve equation: If log ₁₀ Y> -2.4x + 3.7 and does not cross, the film is too rough, the reason quality It is not preferable because it lacks sharpness, the ink is not transferred uniformly, and the resolution is deteriorated, and the end faces become uneven in the cassette. Furthermore, when the number of protrusions having a protrusion height of 0.8 μm is more than 200 / mm ² , the inert solid fine particles fall off and stain the heating head, which is not preferable.

The biaxially oriented polyester film of the present invention has the above-mentioned surface characteristics and has a Young's modulus in the longitudinal direction of 550 to 700.
kg / mm ^2, preferably 600~700kg / mm ^2, 30 at 0.99 ° C.
The heat shrinkage in the longitudinal direction after heat treatment for 3 minutes is required to be 3% or less, and the density must be 1.390 g / cm ³ or less. When the Young's modulus of the film is less than 550 kg / mm ² , the strength is insufficient, so that the film is stretched at the time of transfer, causing perforation and tearing. On the other hand, if the Young's modulus exceeds 700 kg / mm ² , the film is likely to be vertically torn, or the heat shrinkage becomes large, which causes deformation due to heat shrinkage during transfer, which is not preferable. Furthermore, in order to reduce the thermal deformation during transfer, 15
It is necessary that the heat shrinkage in the longitudinal direction when heat-treated at 0 ° C. for 30 minutes is 3% or less. However, in this case the film density
If it exceeds 1.390 g / cm ³ , the stick phenomenon will occur during high-speed printing regardless of the above surface characteristics, which is not preferable. When the film density is 1.390 g / cm ³ or less, the stick phenomenon does not occur surprisingly. The reason for this is not clear, but it is presumed that the voids formed around the inert solid fine particles prevent the polymer from melting due to the temperature rise.

The biaxially oriented polyester film of the present invention is basically produced by melt-casting the above polyester, biaxially stretching it, and further subjecting it to heat treatment. The method or the conditions can be used. More specifically, first, polyester is melted, extruded into a sheet from a slit die, and solidified by cooling with a casting drum to form an unstretched sheet, and the unstretched sheet is stretched at a temperature of 70 to 120.
Stretching is carried out in the machine and transverse directions at a temperature of 3 ° C and a stretching ratio of 3 to 5 times.
The Young's modulus and the density (void amount) can be adjusted by selecting from the longitudinal / transverse stretching ratio and the stretching temperature. After that, heat set at 170 to 260 ° C.

The heat-sensitive transferable coloring layer in the present invention may be a conventionally known heat-transferable coloring layer as it is and is not particularly limited.

The heat-transferable colored layer is a composition containing a colorant and a binder. A dye or pigment is used as the colorant. Examples include inorganic pigments such as carbon black, organic pigments, azo dyes, anthraquinone dyes, and the like. Examples of the binder include waxes such as carnauba wax, wood wax, beeswax, and ester wax, and a composition such as a polymer represented by ethyl cellulose to which a recording accelerator such as dinitrotoluene is added. Various compositions that can be transferred by being softened when heated can be used.
In addition to these, a plasticizer, a softening agent such as oil, and other additives for improving weather resistance may be included. The thickness of the heat-sensitive transfer coloring layer is 0.5 to 20 μm, preferably 0.8 to 10 μm, more preferably 1 to 5 μm. These colored layers are formed by hot-melt coating on a substrate film, or by dispersing or dissolving the composition in a solvent and applying the coating solution.

The transfer material for a thermal transfer printer of the present invention is a biaxially oriented polyester film having a specific surface property and provided with a thermal transfer ink layer, and therefore has no sticking with a heating head and has excellent printability. Since it has higher strength and excellent dimensional stability, it can be formed into a thin film and has good thermal conductivity, and is suitable for high-speed printers and is extremely useful as a small-sized cassette type transfer material.

Various physical properties and characteristics in the present invention are measured and defined as follows.

[I] Characteristics of polyester film (1) Young's modulus measurement The film is cut into a sample width of 10 mm and a length of 15 cm, and the gap between chucks is 100 mm.
mm, and pull at a pulling speed of 10 mm / min and a chart speed of 500 mm / min using an instro type universal tensile tester. The Young's modulus is calculated from the tangent line of the rising portion of the obtained load-elongation curve.

(2) Film density This is a value measured by a float-sink method at 25 ° C. in a mixed solvent of n-heptane and carbon tetrachloride.

(3) Protrusion distribution measurement method Using a three-dimensional roughness meter (SE-3CK) manufactured by Kosaka Laboratory, needle diameter 2 μmR, needle pressure 30 mg, measurement length 1 mm, sampling pitch 2 μm,
Under the conditions of a cutoff of 0.25 mm, a vertical magnification of 20,000 times, a horizontal magnification of 200 times, and 150 scanning lines, the projection profile on the film surface is three-dimensionally (three-dimensionally) imaged.

When the profile is cut in a plane perpendicular to the film thickness, the plane where the total cross-sectional area of the profile of each projection is 70% of the area of the film measurement area is taken as the reference level (0 level), and Let y be the number of projections cut when cut on a plane parallel to the standard level plane and separated by a distance x in the height direction of the projections. A projection distribution curve can be drawn by sequentially increasing or decreasing x, reading the number of y at that time, and plotting it on a graph. The distance x is defined as “protrusion height (x)”, and the above y is defined as “protrusion number (y)”.

(4) Thermal contraction rate Marked lines are put on the measurement sample at intervals of about 30 cm, and it is calculated from the following formula from the change in sample length after heat treatment (150 ° C x 30 minutes) in a heating oven in a tension-free state for a certain period of time.

[II] Characteristics of Transfer Material The characteristics of the transfer material are evaluated as follows.

Each test piece is made into a thermal transfer ribbon by slitting each film with a 6.5 mm width tape, and is put to a thermal printer for practical evaluation.

(5) Stick phenomenon Check whether or not the thermal transfer ribbon and the heating head are fused.

X: Fusing occurs and ribbon conveyance failure is observed. △: Fusing tendency tends to occur, but there is no ribbon conveyance failure and it is acceptable. ○… Slight fusing tendency tends to be good. ◎: No problem at all. Very good (6) Image quality The light and shade of the image printed / printed on the thermal printer was observed.

×: The image has unevenness of light and shade, and bleeding is strong and unusable. △: There is a slight difference in light and shade, there is bleeding, but it is acceptable. ○: Slight bleeding is seen, but there is no light and shade. Very good without bleeding [Examples] Hereinafter, the present invention will be further described with reference to Examples. In addition, "part" in an example means a "weight part."

Example 1 Polyethylene terephthalate pellets having an intrinsic viscosity (orthochlorophenol, 35 ° C.) of 0.620 and containing 0.8% by weight of calcium carbonate having an average particle size of 1.0 μm were dried at 170 ° C. for 3 hours, then fed to an extruder hopper and melted at a melting temperature of 280. Melted at ˜300 ° C., the molten polymer was molded and extruded on a rotating cooling drum to obtain an unstretched film. This unstretched film at 80 ℃
At a temperature of 215 ° C. for 5 seconds to obtain a biaxially oriented film having a thickness of 3.5 μm.

This biaxially oriented film is used as a base film, and 30 parts of carnauba wax and 35 parts of paraffin wax are provided on the upper surface thereof.
Part, oil black HBB (oil-soluble dye manufactured by Orient Chemical Industry Co., Ltd.) 5 parts, carbon black 25 parts and lanolin 5 parts are mixed and heat-melted to a thickness of 4 μm for hot-melt coating, for a thermal transfer printer A transfer material (film) was obtained.

Table 1 shows the characteristics of the biaxially oriented film and the results of evaluating the film for a thermal transfer printer by slitting it to a width of 6.5 mm and applying it to a thermal printer as a thermal transfer ribbon.
The distribution of protrusions on the film surface is as shown by the curve A in FIG. 1, in which case the stick phenomenon did not occur, the running property was good, and the image quality was clear.

Example 2 In the production of the base film of Example 1, 0.6% by weight of calcium carbonate having an average particle size of 1.5 μm and 0.1% by weight of kaolin having an average particle size of 0.8 μm were added as external additives. The characteristics of the obtained biaxially oriented film are shown in Table 1, and the projection distribution curve on the film surface is shown as curve B in FIG. Although the number of high protrusions was slightly increased from that in Example 1, it was a satisfactory film for thermal transfer.

Comparative Examples 1 to 4 The procedure of Example 1 was repeated except that the type and concentration of external additives were changed as shown in Table 1 in the production of polyester film. Table 1 shows the characteristics of the obtained biaxially oriented film and the characteristics of the thermal transfer film. Further, the distribution of protrusions on the surface of the film is shown as curves C, D, E and F in FIG.

In the case of Comparative Example 1 (curve C), the number of protrusions was small over the entire range of the protrusion height, there was a problem of wrinkles during processing, and sticking also occurred during ribbon evaluation, and image quality could not be evaluated. . In the case of Comparative Example 2 (curve D), the stick phenomenon is slightly improved as compared with Comparative Example 1, and the printed image quality is clear, but the stick resistance is practically insufficient. In Comparative Examples 3 and 4 (curves E and F), since the film was rough and there were many high protrusions, the stick phenomenon did not occur, but the ink was not transferred uniformly and the image quality was unclear.

Example 3 and Comparative Examples 5 to 6 In Example 1, the stretching ratios in the machine and transverse directions were adjusted to obtain biaxially oriented films having different Young's moduli. Using this as a base film, a film for a thermal transfer printer was obtained in the same manner as in Example 1. The results of these evaluations are shown in Table 1.
The distribution of protrusions on the film surface was close to curve A.

If the Young's modulus of the film is too low, the film is stretched and deformed during transfer, and if the Young's modulus is too high, shrinkage and deformation is caused during transfer, resulting in defective conveyance of the ribbon.

Example 4 and Comparative Examples 7 to 8 In Example 1, the thickness of the unstretched film was adjusted to obtain biaxially oriented films having different thicknesses. Using this as a base film, a film for a thermal transfer printer was obtained in the same manner as in Example 1. The results of these evaluations are shown in Table 1. The distribution of protrusions on the film surface was close to the curve A in FIG.

As the film becomes thicker, the resolution becomes worse and the image quality becomes unclear. On the other hand, when the film becomes thin, wrinkles are likely to occur during film processing and during running of a thermal printer, and deformation of elongation tends to occur, resulting in conveyance failure and finally fusion to the heating head.

Comparative Example 9 In Example 1, the heat treatment temperature after stretching was adjusted to 150 ° C.
A film having a high longitudinal thermal shrinkage when heat-treated for 30 minutes was obtained. The results of evaluating these are shown in Table 1.

This product had a large shrinkage deformation at the time of transfer, resulting in poor ribbon conveyance, and finally fused to the heating head.

Comparative Example 10 In Example 1, a film was formed under the conditions shown in Table 1 using porous silicon with few voids as an external additive. In this case, there are few voids and the film density is high.

The protrusion distribution curve on the film surface is located between curves A and B in FIG. 1 (omitted), but the stick phenomenon occurred.

[Brief description of drawings]

FIG. 1 is a view showing the relationship between the height of protrusions (x: μm) on the film surface and the number of protrusions (y: number / mm ² ).

Claims (1)

[Claims] 1. A transfer material for a heat-sensitive transfer printer, comprising a biaxially oriented polyester film having a heat-sensitive transferable colored layer which is melted by heating on one surface thereof, wherein the film has (a) a thickness in the range of 2 to 10 μm. , (b) number of protrusions of the film surface (y: number / mm ²⁾ and the projection height (x: [mu] m) maximum greater than value portion of the distribution curve in the distribution curve representing the relationship between the curve formula: 10 g ₁₀ y = -2.4x +
The number of protrusions (Ymax: number / mm ² ) and protrusion height (Xmax: μm) when intersecting at least once with 3.7 and the maximum value of the distribution curve
Relationship formula satisfies 10g ₁₀ Ymax> -2.4Xmax + 3.7, further projection height (x) 0.8 [mu] m of the projections is in the range of 40 to 200 pieces / mm ^2, (c) vertical Young's modulus Is in the range of 550 to 700 kg / mm ² , (d) the heat shrinkage in the longitudinal direction when heat-treated at 150 ° C for 30 minutes is 3% or less, and (e) the density is 1.390 g / cm ³ or less. A transfer material for a thermal transfer printer, which has the following characteristics.