JP2013146876A - Thermal transfer sheet and image forming method using thermal transfer sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thermal transfer sheet high in the thermal transfer efficiency of a dyestuff.SOLUTION: A thermal transfer sheet 11 includes a dyestuff layer 3 having a thermal transfer dyestuff and a binder resin as main components on a substrate 2, and the binder resin includes one or two or more resins of cellulose acetate propionate resin, cellulose acetate butylate resin, and ethyl cellulose resin, and a ratio of the weight of the heat transfer dyestuff to one weight of the binder resin in the dyestuff layer is in a range of 2.5-3.5.

Description

The present invention relates to a thermal transfer sheet and an image forming method using the thermal transfer sheet.

  A technique for driving a thermal head based on a data signal of an electronic image and forming a color image on a dedicated image receiving paper is known as a so-called sublimation transfer recording technique. Sublimation transfer recording is an old technology, and the basic technology as the principle of the thermal transfer sheet in the form currently on sale was filed in 1983 (Patent Document 1).

  The principle is that a disperse dye is used as a thermal transfer dye, and the dye is kept in a dissolved state in a binder in order to increase recording sensitivity. On the other hand, since the disperse dye has a crystalline state that is more thermally stable than the dissolved state, the disperse dye tends to crystallize and precipitate over time, and a binder is required to prevent the disperse dye from precipitating.

  If a resin with a high affinity for the disperse dye is selected as the binder, crystallization and precipitation can be prevented, but the dye dyed amount is distributed between the receiving layer resin of the image receiving paper during heating of the printing paper. A large amount of dye remains in the resin of the thermal transfer sheet having high affinity for the dye, which is not preferable.

  However, since resins having no affinity for disperse dyes cause disperse dyes to precipitate immediately, polyvinyl butyral resins having high Тg have been selected and used from various resins. Since then, polyvinyl acetal resin with a higher Тg has been developed and has been used today as a binder for thermal transfer sheets. At that time, cellulosic resins were known to have high recording sensitivity, but were not employed because they had poor storage stability than polyvinyl butyral resins.

  There have been various technological advances in sublimation transfer recording technology. For example, at that time, sublimation dyes were only disperse dyes for dyeing polyester fibers in a hot water bath. Among them, dyes that were soluble in solvents with relatively high sublimation properties were selected and used. Thermal transfer dyes are designed exclusively for transfer recording technology, and dyes that take into consideration the affinity with the binder are also used.

  At that time, thermal heads were only used for thermal recording paper and melt transfer recording, and there was not enough to apply the amount of heat necessary for sublimation transfer. There is.

  Further, the image receiving sheet as a heat-transferable sheet has been devised such as providing a heat insulating layer and a cushion layer in order to increase recording sensitivity, and sublimation transfer recording can be performed with less energy.

  As for the usage environment, it was originally assumed that the printer for home use was used, and the specifications were adopted so that the performance of the thermal transfer sheet did not change even in harsh environments, but now it is a print sealer and Photo Lucio (registered trademark) ) The use of business printers such as output terminals has become the mainstream, and the usage environment can be controlled to some extent, and it is possible to review the specifications of thermal transfer sheets that do not assume storage stability under harsh conditions .

  For commercial use, there is a high demand for cost reduction, and from the viewpoint of efficient use of dyes, it has been necessary to review the binder of thermal transfer sheets having high dye transfer efficiency based on the above-mentioned technological advances.

  Patent Document 2 describes a thermal transfer sheet using ethyl cellulose having a specified ethoxyl content as a binder.

Japanese Patent Publication No. 7-29504 Special table 2008-524027 gazette

  It is an object to obtain a thermal transfer sheet having high dye transfer efficiency and good storage stability.

  A first invention is a thermal transfer sheet having a dye layer mainly composed of a thermal transferable dye and a binder resin on a substrate, wherein the binder resin is a cellulose acetate propionate resin, a cellulose acetate butyrate resin, It consists of any one or two or more kinds of ethyl cellulose resins, and the weight ratio of the heat transferable dye to the binder resin weight 1 in the dye layer is in the range of 2.5 to 3.5. It is a thermal transfer sheet.

  A second invention is a thermal transfer sheet having a dye layer mainly composed of a thermal transferable dye and a binder resin on a substrate, wherein the binder resin is a cellulose acetate propionate resin or a cellulose acetate butyrate resin. It consists of any one or two of these resins, and the weight ratio of the heat transferable dye to the binder resin weight 1 in the dye layer is in the range of 2.5 to 3.5. It is a thermal transfer sheet as described in the invention.

  A third invention is the thermal transfer sheet according to the first invention or the second invention, wherein the weight ratio of the cellulose acetate propionate resin and the cellulose acetate butyrate resin is 3 to 1.

  4th invention is a thermal transfer sheet as described in any one of 1st invention-3rd invention characterized by the application quantity of a dye layer being 0.25-0.35 g / square meter. It is.

  According to a fifth aspect of the present invention, the dye transfer surface of the thermal transfer sheet and the image receiving layer surface of the sublimation transfer image receiving sheet are overlapped, and the thermal transfer sheet and the sublimation transfer image receiving sheet are sandwiched between a thermal head and a platen roll while applying pressure. In the image recording method of moving, supplying energy based on the image signal to the heating element of the thermal head, and heating the back surface of the thermal transfer sheet to record the image on the sublimation transfer image receiving sheet, the first to fourth inventions Using the thermal transfer sheet described in any one of the inventions, an image recording method is characterized in that printing is performed at a feed rate of one line of 1.0 milliseconds or less.

  A thermal transfer sheet having high dye transfer efficiency and good storage stability can be obtained.

Schematic diagram of sublimation transfer recording method

  Patent Document 1 describes that printing of 4.5 milliseconds is necessary to obtain the maximum density. In addition, it was described in the storage test that a thermal transfer sheet that did not cause a problem after an accelerated test at 60 ° C. for 2 months was required. The resolution of the thermal head available at that time was 150 dpi.

  Many of the commercial printers currently in operation have a thermal head resolution of 300 dpi, a dot size of 80 μm, and a maximum thermal energy applied to one dot of 0.05 mJ to 0.5 mJ. The maximum voltage applied to the thermal head 1 line is 0.7 milliseconds to 2.0 milliseconds.

<Embodiment of the Invention>
The thermal transfer sheet according to the first aspect of the present invention, which can obtain a high recording density within the range of the printing conditions and the storage conditions and has good storage stability, has a thermal transferable dye and a binder resin on a substrate. The binder resin is composed of one or more of cellulose acetate propionate resin, cellulose acetate butyrate resin, and ethyl cellulose resin. The thermal transfer sheet is characterized in that the weight ratio of the thermal transfer dye to the binder resin weight 1 in the dye layer is in the range of 2.5 to 3.5.

  According to a second aspect of the present invention, there is provided a thermal transfer sheet having a dye layer mainly composed of a thermal transferable dye and a binder resin on a substrate, wherein the binder resin comprises cellulose acetate propionate resin, cellulose acetate butyrate. The weight ratio of the thermal transferable dye to the binder resin weight 1 in the dye layer, which is composed of any one or two of the rate resins, is in the range of 2.5 to 3.5. It is a thermal transfer sheet as described in 1 invention.

  A third aspect of the present invention is the thermal transfer sheet according to the first aspect or the second aspect, wherein the weight ratio of the cellulose acetate propionate resin and the cellulose acetate butyrate resin is 3 to 1. It is.

  According to a fourth aspect of the present invention, in any one of the first to third aspects, the coating amount of the dye layer is 0.25 to 0.35 g / square meter. This is a thermal transfer sheet.

  According to a fifth aspect of the present invention, a dye transfer surface of a thermal transfer sheet and an image receiving layer surface of a sublimation transfer image receiving sheet are overlapped, and the thermal transfer sheet and the sublimation transfer image receiving sheet are sandwiched between a thermal head and a platen roll. In the image recording method of recording the image on the sublimation transfer image receiving sheet by supplying energy based on the image signal to the heating element of the thermal head and heating from the back surface of the thermal transfer sheet 4. An image recording method, wherein printing is performed at a feeding speed of one line or less using the thermal transfer sheet described in any one of the four aspects.

  In the schematic diagram of the sublimation transfer recording method of FIG. 1, a heat insulating layer and a cushion layer are provided as the sublimation transfer image receiving sheet, but the present invention is not necessarily limited to the use of the sublimation transfer image receiving sheet having this structure. . In order to print using the thermal transfer sheet of the present invention, a substrate and a receiving layer coated thereon may be provided as a sublimation transfer image receiving sheet.

When considering the dye / binder ratio with high dye transfer efficiency, cellulose acetate butyrate is the most effective for increasing transfer efficiency as a dye binder when the ratio of dye to binder is a specific ratio. The present inventors have found that acetate propionate is most effective for ensuring storage stability, and have reached the present invention.
In addition, you may add arbitrary additives in the ink composition which forms a thermal transfer layer as needed.

<Configuration of thermal transfer sheet>
Hereinafter, materials that can be used for the thermal transfer sheet of the present invention will be described.
(1) Substrate A polyester film is suitable as the substrate on which the ink is applied. A polyester film suitable for this application has been manufactured. Polyester films having thicknesses of 3.0 μm, 3.5 μm, 4.5 μm, 6.0 μm, 9.0 μm and the like are on the market, and are appropriately selected according to the intended use.

(2) Heat-resistant slipping layer For both sublimation transfer recording and melt transfer recording, a thermal film is heated and printed on a thin polyester film coated with a thermal transferable dye or wax, so the thermal head and the transfer film melt with heat. A heat resistant slipping layer is provided on the film so as not to be worn. Since sublimation transfer recording requires a higher amount of heat than melt transfer recording, it is usually manufactured based on the following design concept.

  The heat resistant slipping layer is composed of a crosslinkable resin and an additive. For the crosslinkable resin to withstand high heat, it is necessary to select a resin that has high heat resistance and to have a high degree of crosslinking. Polyvinyl butyral resin and polyfunctional A combination of isocyanates is preferably utilized. Since the heat resistant slipping layer is cured at a high temperature in a wound state after coating, there is usually a blocking problem that the film adheres. The added slip agent solves the problem. In addition to the anti-blocking performance, the slip agent does not bleed the dye even when it comes into contact with the dye layer. Therefore, it is required to have a performance for preventing burn-in with the thermal head and a performance for preventing generation of waste. Among various additives, phosphate surfactants are preferably used. The preferred thickness of the heat resistant slipping layer is 0.1 g / square meter to 2.0 g / square meter. A more preferable thickness is 0.2 g / square meter to 1.0 g / square meter.

(3) Thermal transfer dyes Various dyes have been developed as thermal transfer dyes used for sublimation transfer recording. For example, as a cyan dye, for example, there is a dye having a structure of Compound 1.

Examples of the magenta dye include a dye having a structure of Compound 2.

As the yellow dye, for example, there is a dye having a structure of Compound 3.

  In addition to the dyes developed for the present technology as described above, there are also disperse dyes that have been used for a long time and are still added and used. When these disperse dyes are added to the thermal transfer sheet, the storage stability of the thermal transfer sheet depends on the performance of the disperse dye. That is, the disperse dye often precipitates before the developed new dye is precipitated. Therefore, the thermal transfer sheet storage test is conducted by adding a disperse dye in addition to the developed dye.

(4) Dye binder As the dye binder, ethyl cellulose resin, cellulose acetate propionate resin, and cellulose acetate butyrate resin were studied and selected. The dye transfer efficiency and storage stability were evaluated by the following methods as a single resin or by mixing resins.

(5) Dye layer In the conventional thermal transfer sheet, the preferred thickness of the dye layer was 0.8 g / m 2 to 1.2 / m 2, but because the amount of the dye is less than the amount of the binder, It was thick.

  In the thermal transfer sheet of the present invention, the weight ratio of the heat transferable dye to the binder resin weight of 1 in the dye layer is preferably in the range of 2.0 to 3.7, and the weight ratio of the heat transferable dye is 2.5 to 3. A range of 5 is particularly preferred.

  A preferable coating amount range of the thermal transfer sheet of the present invention in which the preferable ratio of the thermal transfer dye and the binder is within the above range is 0.20 g / square meter to 0.40 g / square meter. Furthermore, 0.25 g / square meter to 0.35 g / square meter is particularly preferable.

<Preparation of sublimation transfer image receiving sheet>
A method for producing a sublimation transfer image receiving sheet used in combination with the thermal transfer sheet of the present invention will be described below.

  An adhesive layer forming ink having the following composition was applied to one surface of a 39 μm-thick microvoided film of the fine void layer and dried to form an adhesive layer. Next, the support provided with the back layer on one side of the coated paper (186 g / square meter) and the microvoid film are so arranged that the surface opposite to the side provided with the back layer of the support overlaps the adhesive layer. Pasted together.

Adhesive layer forming ink:
Polyfunctional polyol “Takelac (registered trademark) A-969V” 30.0 parts by weight
(Mitsui Chemicals)
Isocyanate “Takenate (registered trademark) A-5” 10.0 parts by weight
(Mitsui Chemicals)
60.0 parts by weight of ethyl acetate

  Subsequently, a primer layer forming ink having the following composition was applied to the surface opposite to the surface provided with the adhesive layer of the microvoid film by wire bar coating so that the dry coating amount was 2.0 g / square meter. The primer layer was formed by drying.

Ink for primer layer formation:
Polyester polyol "Adcoat (registered trademark)" 15.0 parts by weight
(Toyo Morton Co., Ltd.)
Methyl ethyl ketone / toluene (weight ratio 2: 1) 85.0 parts by weight

  On the formed primer layer, a dye receiving layer forming ink having the following composition is applied by wire bar coating so that the dry coating amount is 4.0 g / m 2, and dried to form a dye receiving layer. Sublimation transfer image receiving sheet 1 was obtained.

Dye-receiving layer forming ink:
20.0 parts by weight of vinyl chloride-vinyl acetate copolymer resin (vinyl chloride / vinyl acetate = 87/13, number average molecular weight 31,000,
Glass transition temperature 70 ° C.) “Solvine C (registered trademark) manufactured by Nissin Chemical Industry Co., Ltd.”
Carboxyl-modified silicone 1.0 part by weight (X-22-3701E, manufactured by Shin-Etsu Chemical Co., Ltd.)
Methyl ethyl ketone / toluene (weight ratio 1: 1) 79.0 parts by weight

<Evaluation method of thermal transfer sheet>
(1) Evaluation Method of Dye Transfer Efficiency Using the following thermal transfer sheet and the sublimation transfer image receiving sheet 1 prepared as described above, an evaluation printer (resolution 300 dpi, head resistance value 5300Ω, applied voltage: 25.5 V) A solid print of a predetermined color is created at a print line speed of 1.0 ms / line and a pulse duty of 85%. A printed matter evaluated at the maximum density of 255 gradations of the printed matter (= tone value is 255/255) was prepared, and a thermal transfer sheet from which the dye was removed was obtained.

The thermal transfer sheet used for printing and the unused thermal transfer sheet are cut into 5 cm x 5 cm, and the dye is extracted with a one-to-one solvent of toluene / methyl ethyl ketone. Using high performance liquid chromatography (Shimadzu LC-2010HТ) The dye content was measured.
From the obtained dye content, the transfer efficiency was calculated by the following formula 1.
The higher the transfer efficiency, the more effectively the dye is used.

(2) Method for evaluating storage stability of thermal transfer sheet Using the following thermal transfer sheet and the previously produced sublimation transfer image-receiving sheet 1, white solid pattern (= gradation value 0 / 255).
On the other hand, the following unprinted thermal transfer sheet was stored at 40 ° C. and 90% for 100 hours to produce a printed product with a white solid pattern in the same manner as above.

The L * a * b * value of the printed matter was measured using a color difference meter (Spectrolino) manufactured by X-Lite.
In Equation 2 below, the color difference (ΔE) between the print using the thermal transfer sheet subjected to the storage test and the print using the thermal transfer sheet not subjected to the storage test is calculated, and the value is used as the evaluation of the storage stability. . The smaller the color difference, the better the storage stability.

<Preparation of thermal transfer sheet>
A dye layer having the following composition was applied to the opposite surface of the 4.5 μm thick polyester film provided with the heat-resistant slip layer and dried. Each transfer film was evaluated by the above transfer efficiency evaluation method and storage stability evaluation method.
A magenta dye having the following composition was used in all examples and comparative examples.

Compound 4 Dye 2.0 parts by weight Compound 5 (Disperse Red 60) 2.0 parts by weight Compound 6 (Disperse Violet 26) 3.0 parts by weight Binder resin 2.8 parts by weight Toluene / methyl ethyl ketone (one-to-one mixed solvent) 100 parts by weight

  The above ink composition is a composition when the weight ratio of the dye to the binder is 2.5 to 1. When inks having different weight ratios of the dye and the binder were prepared, the ink was prepared and used at a predetermined weight ratio by appropriately increasing or decreasing the amount of the binder resin and the amount of the mixed solvent.

As the binder resin, the following resins were used.

Cellulose acetate butyrate resin (Eastman Chemical Co., CAB171-15S)
Cellulose acetate propionate resin (Eastman Chemical Co., CAP482-0.5)
Ethyl cellulose resin (Eastman Chemical Co., SТD-45)
Polyvinyl acetal resin (Sekisui Chemical Co., Ltd., ESREC (registered trademark) KS-5)

Examples 1 to 3 in Table 1 show the results using cellulose acetate butyrate resin, cellulose acetate propionate resin, and ethyl cellulose resin alone as a binder. Moreover, the result when a cellulose acetate butyrate resin and a cellulose acetate propionate resin are mixed and used as a binder is shown in Examples 4 to 6. Furthermore, as Comparative Example 1, the results when a polyvinyl acetal resin is used as a binder are shown.
All dye to binder ratios are 2.5 to 1, and the dry coverage of the dye layer is 0.35 g / square meter.

When polyvinyl acetal resin was used as a binder, the transfer efficiency was as low as 73.2%, while the transfer efficiency of all others was good at 80% or more.
Further, as Comparative Example 2, a thermal transfer sheet in which the ratio of the dye to cellulose acetate butyrate resin was 2.0 improved the storage stability, but the transfer efficiency was 80% or less.

Table 2 shows the results of Example 7, Example 1, and Example 8 in which the coating amount was changed using cellulose acetate butyrate resin as a binder. In all cases, the dye to binder ratio is 2.5 to 1.
When the coating amount of the dye layer is increased, the storage stability is improved, but the transfer efficiency is lowered. When the coating amount of the dye layer is 0.40 g / square meter, the transfer efficiency is 80% or less.

Table 3 shows the results of Example 9, Example 2, and Example 10 in which the coating amount was changed using cellulose acetate propionate resin as a binder. In all cases, the dye to binder ratio is 2.5 to 1.
When the coating amount of the dye layer is increased, the storage stability is improved, but the transfer efficiency is lowered. When the coating amount of the dye layer is 0.40 g / square meter, the transfer efficiency is 80% or less.

  Table 4 shows Examples 11 to 13 of the test results in which the ratio of the dye and the binder was increased to 3.5 to 1, using cellulose acetate butyrate resin, cellulose acetate propionate resin, and ethyl cellulose resin alone as a binder. Show. The coating amount of the dye layer is 0.35 g / square meter. Although storage stability is lowered, transfer efficiency is improved and good.

Table 5 shows the results of Examples 14 to 16 when ethyl cellulose resin and cellulose acetate propionate resin are mixed and used as a binder. In all cases, the dye to binder ratio is 2.5 to 1. The dry coating amount of the dye layer is 0.35 g / square meter.
All have a transfer efficiency of 80% or more and good storage stability.

Table 6 shows the results of Examples 17 to 19 when ethyl cellulose resin and cellulose acetate butyrate resin are mixed and used as a binder. In all cases, the dye to binder ratio is 2.5 to 1. The dry coating amount of the dye layer is 0.35 g / square meter.
All are good with a transfer efficiency of 80% or more.

  A gradation pattern was printed with a printer DS40 manufactured by DNP Photo Lucio Co., Ltd., using the sublimation transfer image-receiving sheet 1 previously prepared as the thermal transfer sheet of Example 1. The highest concentration was 2.25. Densitometer ND-11 manufactured by Nippon Denshoku Industries Co., Ltd. was used as the densitometer. The feed rate for one line is 1 millisecond.

  As the thermal transfer sheet of Example 7, the sublimation transfer image-receiving sheet 1 previously prepared was used, and a gradation pattern was printed by a printer DS40 manufactured by DNP Photo Lucio. The highest concentration was 2.10. The feed rate for one line is 1 millisecond.

  The application amount of the dye on the thermal transfer sheet of Example 7 was changed to 0.20 g / square meter, and the gradation pattern was printed with the printer DS40 manufactured by DNP Photo Lucio Co., Ltd., using the sublimation transfer image-receiving sheet 1 previously prepared. . The maximum density is 1.85, which is 2.00 or less and cannot be used. The feed rate for one line is 1 millisecond.

  In Example 7 described in Patent Document 1, the ratio of the dye to the binder is 1: 1.76, the coating amount of the dye layer is 1.0 g / square meter, and the amount of the dye per square meter is 0. .36 g / square meter. The amount of the dye of Example 1 of the present invention is 0.25 g / square meter, and it can be seen that a high recording density is obtained even if the amount of the dye used is small.

  The thermal transfer sheet having the constitution of the present invention can provide a high printing density even when the amount of the thermal transfer dye used is reduced, and can be used in a wide range of industrial applications because it can record at a high speed.

1: Heat-resistant slip layer 2: Substrate (film)
3: Dye layer 4: Receptive layer 5: Cushion layer 6: Heat insulation layer 7: Substrate 11: Thermal transfer sheet 12: Sublimation transfer image receiving sheet 21: Thermal head 22: Platen roll

Claims (5)

A thermal transfer sheet having a dye layer mainly composed of a thermal transferable dye and a binder resin on a substrate,
The binder resin is composed of one or more of cellulose acetate propionate resin, cellulose acetate butyrate resin, and ethyl cellulose resin,
A thermal transfer sheet, wherein the weight ratio of the thermal transfer dye to the binder resin weight 1 in the dye layer is in the range of 2.5 to 3.5. A thermal transfer sheet having a dye layer mainly composed of a thermal transferable dye and a binder resin on a substrate,
The binder resin is composed of any one or two of cellulose acetate propionate resin and cellulose acetate butyrate resin,
2. The thermal transfer sheet according to claim 1, wherein the weight ratio of the thermal transfer dye to the binder resin weight of 1 in the dye layer is in the range of 2.5 to 3.5. 3.   The thermal transfer sheet according to claim 1 or 2, wherein the weight ratio of the cellulose acetate propionate resin and the cellulose acetate butyrate resin is 3 to 1.   The thermal transfer sheet according to any one of claims 1 to 3, wherein the coating amount of the dye layer is 0.25 to 0.35 g / square meter. The surface of the thermal transfer sheet coated with the dye and the receiving layer surface of the sublimation transfer image receiving sheet are overlapped, and the thermal transfer sheet and the sublimation transfer image receiving sheet are sandwiched between the thermal head and the platen roll and moved while applying pressure. In an image recording method of supplying energy based on an image signal to a heating element and heating the back surface of a thermal transfer sheet to record an image on a sublimation transfer image receiving sheet,
5. An image recording method, wherein the thermal transfer sheet according to claim 1 is used to perform printing at a feed rate of one line of 1.0 milliseconds or less.

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