JP3213380B2 - Thermal transfer sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal transfer sheet, and more particularly, to a thermal transfer method (hereinafter, referred to as an N-fold mode method) in which the transfer speed of a transfer object is set higher than the transfer speed of a thermal transfer sheet.
The present invention relates to a thermal transfer sheet used for the above.

[0002]

2. Description of the Related Art Conventionally, when an output print of a computer or a word processor is performed by a thermal transfer method, a thermal transfer sheet provided with a heat-meltable ink layer on one surface of a base film has been used. This heat transfer sheet is composed of a heat-resistant base film having heat resistance and a hot-melt ink layer formed by applying and drying a hot-melt ink obtained by mixing a coloring agent such as a pigment or a dye with wax on the base film. It is provided.

However, such a conventional thermal transfer sheet can perform only one printing at the same location, and therefore, the thermal transfer sheet having the same length as the total length of the printed image is consumed, and the running cost is reduced. There was a problem of becoming larger.

[0004] As one method of solving such a problem, a thermal transfer sheet for multiple printing, which can be printed a plurality of times at the same location, has been developed. However, when printing is performed using the thermal transfer sheet for printing many times, the printing density gradually decreases as the number of printings increases, and there is a problem that printing with uniform density is difficult.

As another method for solving the above-mentioned problem, a so-called N-times mode method has been developed in which printing is performed with the transfer speed of the transfer-receiving member set higher than the transfer speed of the thermal transfer sheet. In the N-fold mode method, the transfer direction of the transfer target and the transfer direction of the thermal transfer sheet may be the same direction or the opposite direction. The transfer speed of the transfer target is N, and the transfer speed of the thermal transfer sheet is N ′ (here, , N> N '), the printing distance is N and the consumption of the thermal transfer sheet is N'. For example, if N = 5 and N '= 1, the consumption of the thermal transfer sheet is 1/5 of that of the conventional thermal transfer method.
It is very economical.

[0006]

However, the thermal transfer sheet used in the conventional N-fold mode method has a problem in that good printing cannot be performed on an object to be transferred having low surface smoothness such as rough paper. Was. That is, irregularities due to fibers are formed on the surface of the rough paper, and in printing by the N-fold mode method, when the ink is melted and transferred to the rough paper, the convex portion of the rough paper and the base film of the thermal transfer sheet are removed. Rubbing occurs during printing, the transferred ink is sheared and enters into the recesses between the fibers, and the fibers that constitute the projections of the rough paper are exposed, resulting in insufficient print density. Will be.

In order to solve this problem, for example, in a thermal transfer sheet for black printing, a so-called chip pigment obtained by kneading carbon and an ethylene-vinyl acetate copolymer (EVA) is contained in an ink layer in a large amount. ing. However, although the blackness of the ink itself is improved by adding such a chip pigment, the exposure of the fibers in the printed portion is not solved, and the blackness of the printed image is not improved. In addition, a method has been proposed in which a large amount of EVA having a low melt flow rate (MFR) is contained in ink to prevent fiber exposure and achieve high-density printing, but this method has too high a viscosity. For this reason, there has been a problem that the sensitivity is lowered and that printing with good halftone cannot be performed.

[0008] The present invention has been made in view of such circumstances, and even when the transfer target used in the N-fold mode method has a low surface smoothness such as rough paper, the print density is sufficient. An object of the present invention is to provide a thermal transfer sheet for the N-times mode, which is capable of performing high thermal transfer with good halftone.

[0009]

In order to achieve the above object, the present invention has a base film and an ink layer formed on one surface of the base film, and has a temperature of 75%.
The storage elastic modulus (E ') of the ink layer is 3.5 × 10 ³ dyn / cm ² or more and the loss elastic modulus (E ″) is 7.0 × 10 ³ dyn / cm ^{2 in} the range of -100 ° C. And the ratio (E ′ / E ″) of the numerical values of the storage elastic modulus (E ′) and the loss elastic modulus (E ″) is 1.2 or more, and the transport speed of the object to be transferred is the transport speed of the thermal transfer sheet. The present invention also provides a thermal transfer sheet characterized by being used for a thermal transfer method carried out as a larger than the above.The present invention also provides a substrate film, and an ink layer formed on one surface of the substrate film. Has,
The storage elastic modulus (E ') of the ink layer is 3.5 × 10 ³ dyn / cm ² or more in a temperature range of 75 to 100 ° C.,
The loss elastic modulus (E ″) is 7.0 × 10 ³ dyn / cm ² or less, and the ratio (E ′ / E ″) between the storage elastic modulus (E ′) and the loss elastic modulus (E ″) is 1 The present invention provides a thermal transfer method using a thermal transfer sheet having a transfer speed of at least 2 and making the transport speed of an object to be transferred higher than the transport speed of the thermal transfer sheet.

[0010]

The ink layer has a physical property in the temperature range of 75 to 1
At 00 ° C., the storage modulus (E ′) is 3.5 × 10 ³
dyn / cm ² or more, and the loss elastic modulus (E ″) is 7.0 × 1
0 ³ dyn / cm ² or less, and the ratio of the two values (E ′
/ E ″) is 1.2 or more, the melted portion of the ink layer heated by the thermal head has a low elasticity while exhibiting a high elastic modulus. The image is transferred so as to cover the convex portion of the object to be transferred, a sufficient print density is obtained, and printing with high sensitivity and good halftone can be performed.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic sectional view of the thermal transfer sheet of the present invention. In FIG. 1, the thermal transfer sheet 10 includes a base film 11, an ink layer 12 formed on one surface of the base film 11, and a surface layer 13 provided on the ink layer 12.

As the substrate film 11, a substrate film used for a conventional thermal transfer sheet can be used as it is, and is not particularly limited. For example, plastic films such as polyester, polypropylene, cellophane, polycarbonate, cellulose acetate, polyethylene, polyvinyl chloride, polystyrene, nylon, polyimide, polyvinylidene chloride, polyvinyl alcohol, fluororesin, chlorinated rubber, and ionomer, condenser paper, paraffin paper, etc. Papers and nonwoven fabrics are preferably used. Further, these composites can also be used as a base film.

The thickness of such a base film can be appropriately determined so as to obtain required strength and thermal conductivity, and is, for example, about 2 to 25 μm. Ink layer 1
No. 2 consists of a binder, a coloring agent, and various additives added as required.

In the thermal transfer sheet of the present invention, the ink layer 12 has a storage elastic modulus (E ') of 3.5 × 10 ³ dyn / cm ² or more, preferably 5.0 × 10 ^{3 at a} temperature range of 75 to 100 ° C. ³ dyn / cm ² or more, and the loss elastic modulus (E ″) is 7.0 × 10 ³ dyn / cm ² or less, preferably 6.0 × 10 ³ dyn / cm ² or less, and a numerical value of both. (E ′ / E ″) is 1.2 or more, preferably 1.4 or more. Since the ink layer 12 has such characteristics, even if the thermal head immediately after printing is started is in a relatively low temperature state, the melted portion of the ink layer has a high elastic modulus and a low viscosity state. On the other hand, when the thermal head is sufficiently heated, the heated portion of the ink layer 12 that is heated exhibits stable viscoelasticity without a decrease in elasticity. In addition, high print density and good halftone thermal transfer can be achieved.

Here, the storage elastic modulus (E ') and the loss elastic modulus (E ") of the ink layer 12 are measured as follows: (Measurement method) Measuring machine: Toyo Seiki Seisakusho Co., Ltd. Rheographic sol Measurement range: 70-100 ° C Temperature drop rate: 2 ° C / min Measurement interval: 1 ° C In the present invention, in order to form such an ink layer 12, for example, styrene-butadiene-styrene is contained in a binder of the ink layer 12. Block copolymer (SBS), styrene-ethylene / butylene-styrene block copolymer (SEBS), styrene-isoprene-styrene block copolymer (SIS), butadiene rubber (BR), styrene-butadiene block copolymer ( SBR), isoprene rubber (IR), nitrile butadiene rubber (NB
R), synthetic rubber such as chloroprene acrylo rubber (CR) and acrylic rubber (ACM, ANM). That is, the binder used for the ink layer 12 can be composed of wax, the above-described synthetic rubber, and further necessary additives. In this case, the content of the synthetic rubber in the ink layer 12 is preferably about 1 to 15% by weight. If the content is less than 1% by weight, sufficient viscoelasticity cannot be obtained, high printing density cannot be achieved, and the content is 15% by weight.
If the amount is more than 10% by weight, the sensitivity of the thermal transfer sheet is lowered, and tailing is likely to occur due to the entanglement of the transferred ink, so that good halftone printing cannot be performed.

The wax used as a binder for the ink layer 12 includes microcrystalline wax,
Carnauba wax, paraffin wax, Fischer-Tropsch wax, various low molecular weight polyethylene, wood wax, beeswax, whale wax, ibota wax, wool wax, shellac wax, candelilla wax, petrolactam, partially modified wax, fatty acid ester, fatty acid amide, etc. Various waxes can be used.

As the coloring agent used in the ink layer 12, among organic or inorganic pigments or dyes, those having a sufficient coloring density and not discoloring by light, heat or the like are preferably used. Various colors such as cyan, magenta, and yellow can be used. Since the ink layer 12 prints N times with an ink layer having a relatively small area, the colorant concentration needs to be set relatively high. For example, the thickness of the ink layer 12 is in the range of 3 to 20 μm. , The colorant concentration in the ink layer 12 is 1
It is about 5 to 50% by weight, preferably about 20 to 40% by weight. If the concentration of the colorant is less than 15% by weight, the print density is not sufficient, and if the concentration of the colorant exceeds 50% by weight, wetting of the ink on the transfer receiving body becomes poor, and voids are easily generated, which is not preferable.

The surface layer 13 may be formed of, for example, the above-described wax used for the ink layer 12, or may be formed of a binder used for the ink layer 12. Furthermore, it is formed with a lubricant such as a lubricating wax, a silicone wax, a fluororesin, a silicone resin, a higher fatty acid amide, a higher fatty acid ester, and a surfactant, or a thermoplastic resin is added to these lubricants to increase the film strength. The surface layer may have a two-layer structure of a lubricant layer and a thermoplastic resin layer. Such a surface layer 13
Is preferably about 0.1 to 5 μm.

Further, in the present invention, a sensitivity increasing layer may be provided between the ink layer 12 and the surface layer 13. It is preferable to blend this sensitivity increasing layer using a binder used for the ink layer 12 so that the melt viscosity at 100 ° C. becomes lower than that of the ink layer 12. The thickness of the sensitivity enhancement layer is about 0.1 to 5 μm, preferably 0.5 to 3 μm.
m, and when the sensitivity-up layer is too thin, a sufficient sensitizing effect cannot be obtained, and when it is too thick, the density decreases, which is not preferable.

Next, the present invention will be described in more detail with reference to experimental examples. (Experimental Example) First, coating solutions (16 types from I-1 to I-16) for an ink layer having the following composition were prepared. Here, the synthetic rubber A used in the coating liquid for each ink layer was used.
The product name, parts by weight B, and the content in the ink layer were as shown in Table 1.

(Composition of coating liquid for ink layer) Carbon black: 40 parts by weight Ethylene-vinyl acetate copolymer (manufactured by Sumitomo Chemical Co., Ltd.): 10 parts by weight Ethylene-maleic acid copolymer (Mitsubishi) 20 parts by weight-150 ° F paraffin wax ... 45 parts by weight-Carnauba wax ... 10 parts by weight-Synthetic rubber A ... B parts by weight As shown in Table 1, instead of synthetic rubber And two coating liquids (I-17 and I-18) were prepared using an ethylene-vinyl acetate copolymer (EVA).

Table 1 shows the results of measuring the storage elastic modulus and the loss elastic modulus at 75 ° C. and 100 ° C. of each of the ink layer coating liquids. Further, for the ink layer coating liquids I-1, I-2, and I-3 and the ink layer coating liquids I-9, I-10, and I-11 as comparative examples, the storage elastic modulus and the temperature change with respect to temperature change were measured. The change in the loss modulus was measured according to the method described above, and the results are shown in FIGS.

[0023]

[Table 1] Next, the above coating liquid for each ink layer was applied to the surface of a 6 μm-thick polyester film (Lumirror manufactured by Toray Industries, Inc.) as a base film by a gravure roll coating method (coating amount = 10 g / m ² ( (During drying)) and dried to form an ink layer.

Then, a coating liquid for a surface layer having the following composition is applied onto the ink layer by a gravure roll coating method (coating amount = 1.2 g / m ² (when dried)) and dried to form a surface layer. Thus, a thermal transfer sheet (Sample 1 to Sample 18) was obtained.

(Composition of surface layer coating liquid) Carnauba wax: 45 parts by weight 150 ° F. paraffin wax: 30 parts by weight Ethylene-vinyl acetate copolymer: 60 parts by weight Amido wax: 5 parts by weight The thermal transfer sheets (samples 1 to 18) formed as described above were transferred to rough paper by the N-fold mode method and evaluated for blackness, sensitivity, and halftone under the following conditions.
It was shown to.

(Conditions for N-times mode method) Evaluator: N-times mode evaluator made by NP N value: 4 (Evaluation condition of blackness) The solid black portion of the electrophotographic chart No. 2 was measured with a Macbeth reflection densitometer by 10 The points were measured, and the average value was measured.

(Evaluation conditions for sensitivity) 1
A dot horizontal line was printed, and the omission and blurring were visually judged.

[0028] (Evaluation Conditions for Halftone) Photographic image information input to the memory was printed, and its reproducibility and gradation were visually judged.

[0029]

[0030]

[Table 2] As shown in Table 2, the thermal transfer sheet of the present invention (Sample 1
-3, 5-7) have high blackness and high sensitivity, and it is clear that printing can be performed with good halftone by the N-fold mode method even on a transferred material having low surface smoothness. The inks used for each of these samples are shown in Table 1, FIG.
As is clear from FIG. 3, in the temperature range of 75 to 100 ° C., the storage elastic modulus (E ′) is 3.5 × 10 ³ dyn / cm ² or more, and the loss elastic modulus (E ″) is 7.0 × 10 ^3. dyn / cm ² or less, and the ratio (E ′ / E ″) between the two values is 1.2 or more.

However, the thermal transfer sheet in which the viscosity and the elastic modulus of the ink layer do not reach the range of the present invention (Samples 4 and 8)
Was insufficient in blackness. Further, the thermal transfer sheets using EVA instead of synthetic rubber (samples 9 to 13) have high blackness, but low sensitivity, entanglement of the transferred ink, tailing, poor halftone, The blackness and sensitivity were insufficient.

[0032]

As described in detail above, according to the present invention, the molten portion of the ink layer heated by the thermal head is:
Regardless of whether the thermal head after printing is in a relatively low temperature state or in a state where the thermal head is sufficiently heated, the thermal head shows a high elastic modulus and has a low viscosity. Even if the object to be transferred has low surface smoothness such as rough paper, the melted ink is transferred so as to cover the convex portions of the object to be transferred, and the print density is sufficiently high and the halftone is also good. Thermal transfer becomes possible.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a thermal transfer sheet of the present invention.

FIG. 2 is a graph showing a relationship between a temperature, an elastic modulus, and a viscosity of a coating liquid for an ink layer.

FIG. 3 is a graph showing the relationship between the temperature, the elastic modulus, and the viscosity of a coating liquid for an ink layer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Thermal transfer sheet 11 ... Base film 12 ... Ink layer 13 ... Surface layer

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yuichi Kaneko 1-1-1, Ichigaya-Kaga-cho, Shinjuku-ku, Tokyo Inside Dai Nippon Printing Co., Ltd. (72) Inventor Nozomu Hamada 450 Aotomachi, Midori-ku, Yokohama-shi, Kanagawa JP-A-64-40378 (JP, A) JP-A-3-63180 (JP, A) JP-A-2-150386 (JP, A) JP-A-1- 247194 (JP, A) JP-A-62-223072 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41M 5/38-5/40

Claims (4)

(57) [Claims] 1. A base film having an ink layer formed on one surface of the base film, and having a temperature of 75 to 10
In the range of 0 ° C., the storage elastic modulus (E ′) of the ink layer is 3.5 × 10 ³ dyn / cm ² or more, and the loss elastic modulus (E ″) is 7.0 × 10 ³ dyn / cm ² or less. And a ratio (E ′ / E ′) of the numerical values of the storage elastic modulus (E ′) and the loss elastic modulus (E ″).
E ″) is 1.2 or more , and the transfer speed of the transfer
Used for thermal transfer method performed at a speed higher than the transfer speed of the copy sheet
A thermal transfer sheet , characterized in that it can be used . 2. The thermal transfer sheet according to claim 1, wherein the ink layer contains a synthetic rubber as a binder. 3. The thermal transfer sheet according to claim 1, wherein the ink layer contains 1 to 15% by weight of a synthetic rubber. 4. A base film and one of the base films
Having an ink layer formed on the surface of
In the range of 0 ° C., the storage elastic modulus (E ′) of the ink layer is
3.5 × 10 ³ dyn / cm ² or more, loss elastic modulus
(E ″) is 7.0 × 10 ³ dyn / cm ² or less, and
Ratio (E '/ E') and the loss modulus (E ")
E ″) is not less than 1.2,
Set the transfer speed of the body higher than the transfer speed of the thermal transfer sheet
A thermal transfer method, characterized in that: