JPH01114486A - Thermal-transfer sheet - Google Patents

Abstract

PURPOSE:To enable clear thermal transfers in a plurality of times, by a method wherein a plurality of layers of thermally meltable ink are laminated on a base film, in a manner that softening temperature of each layer may be sequentially lowered, through a thermally meltable release layer having a lower melting point than any of those ink layers. CONSTITUTION:Thermally meltable ink layer 2 is formed on a base film 1, the ink layer 2 is composed of ink layer 21, 22, 23-2n. Between the plurality of the ink layers, each thermally meltable release layer 3 having a melting point lower than any of those ink layers is formed, wherein the softening point of each ink layer is made lower as it is away from the base film 1. Further a sticking preventive layer 4 is formed on the other side of the base film 1, and a sealing layer 5 may be formed on an ink layer 2n. When a transfer is effected with the obtained thermal transfer sheet, a definite layer release occurs at the release layer of the lower softening point, and each ink layer is sequentially transferred.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a thermal transfer sheet, and more specifically, an object of the present invention is to provide a novel thermal transfer sheet capable of performing multiple thermal transfers with a single thermal transfer sheet.

(Prior Art) Conventionally, when printing output from a computer or a word processor using a thermal transfer method, a thermal transfer sheet having a base film and a heat-melting ink layer provided on one side has been used.

This conventional thermal transfer sheet uses a paper such as capacitor paper or paraffin paper with a thickness of 8 to 20 μm, or a plastic film such as polyester or cellophane with a thickness of 3 to 20 μm as a base film, and pigments or dyes are added to the wax. It is manufactured by coating a layer of hot-melt ink containing a colorant such as .

When such a thermal transfer sheet as described above is used once, the entire ink layer is thermally transferred in that area, so it cannot be used more than once, and there is a problem in that it is expensive in terms of materials.

As a method to solve this problem, a thermal transfer sheet has been proposed in which a plurality of ink layers are provided on a base film, and each layer is thermally transferred in one thermal transfer, thereby enabling multiple thermal transfers.

(Problem to be Solved by the Invention) In the thermal transfer sheet that can be thermally transferred multiple times, each ink layer is as thin as several μm, and is formed mainly from wax with a relatively low softening point. Therefore, it is difficult to transfer one layer at a time in one thermal transfer, and there is a problem that all layers are thermally transferred at the same time, resulting in poor image quality in the next transfer.

As a method to solve these drawbacks, it has been proposed to change the molecular weight and softening point of the wax used for each layer, but since the softening point of wax that can be thermally transferred is limited to a certain range, It is not possible to use waxes with significantly different molecular weights and softening points, and this has not been a sufficient means of solving the problem.

Therefore, it is an object of the present invention to provide a thermal transfer sheet that can be thermally transferred multiple times using a conventionally known wax or the like without requiring any special means.

(Means for solving problems) The above object is achieved by the present invention as described below.

That is, in the present invention, a plurality of heat-melt ink layers having different softening temperatures are laminated on one surface of a base film via a heat-melt release layer having a lower softening point than these ink layers, These plurality of ink layers are a heat-sensitive transfer sheet characterized by having softening points that decrease successively as they get farther away from the base film.

(Function) When forming multiple ink layers on a base film, these multiple ink layers are sequentially layered through a heat-meltable release layer having a lower softening point than the ink layer, and a layer having a higher softening point than the ink layer. By laminating the ink layer in layers lower than the ink layer, clear layer separation occurs at the release layer with a low softening point during transfer, and each ink layer is sequentially transferred to the receiving paper.

(Preferred Embodiments) Next, the present invention will be described in more detail by citing preferred embodiments.

The heat-sensitive transfer sheet of the present invention has a heat-melting ink layer 2 formed on a base film 1, as shown schematically in a part of its cross section in FIG. ．． ．． 22.2. -2nhm, and between the plurality of ink layers 2, a heat-melting release layer 3 having a softening point lower than that of these ink layers is formed, and the softening point of the ink layer increases as the distance from the base film l increases. Furthermore, an anti-sticking layer 4 may be formed on the other surface of the base film 1, and a surface layer (blocking layer) 5 may be further formed on the ink layer 2n. It is.

For example, an example where the total number of ink layers is 3 (n=3) (
To explain multiple thermal transfers using Figure 1), in the first thermal transfer, as shown in Figure 2, the entire layers 2 and 3 are heated by the thermal head 6 from the back side. In this case, the layer with the lowest softening point is layer 23, and the peeling layer 32 between layer 23 and layer 2 has a softening point lower than any of the ink layers. The 23 layers adhered (via layer 5) peel off at layer 32.

In the second printing, 22 layers are thermally transferred in the same manner as above, and in the third printing, a 2° layer is thermally transferred.

Next, the present invention will be explained in more detail with reference to the material and manufacturing method of the thermal transfer sheet.

As the base film 1 used in the present invention, the same base film used in conventional thermal transfer sheets can be used as is, and other base films can also be used, and there are no particular limitations.

As specific examples of preferable base film 1, for example,
Plastics such as polyester, polypropylene, cellophane, polycarbonate, cellulose acetate, polyethylene, polyvinyl chloride, polystyrene, nylon, polyimide, polyvinylidene chloride, polyvinyl alcohol, fluororesin, chlorinated rubber, ionomer, condenser paper,
Papers such as paraffin paper, nonwoven fabrics, etc. may be used, and base films made of composites of these may also be used.

The thickness of the base film 1 can be changed as appropriate depending on the material so that its strength and thermal conductivity are appropriate, but the thickness is preferably, for example, 3 to 25 mm.
It is μm.

The heat-melting ink layer 2 used in the present invention consists of a colorant and a vehicle, and may further contain various additives as required.

The coloring agent is preferably an organic or inorganic pigment or dye that has good properties as a recording material, for example, one that has sufficient color density and does not discolor or fade due to light, heat, temperature, etc.

Alternatively, it may be a substance that is colorless when not heated but develops color when heated, or a substance that develops color when it comes into contact with something coated on the transfer paper. In addition to the colorants forming cyan, magenta, yellow, and black, colorants of various other colors can also be used.

The vehicle used includes wax as a main component, and mixtures of wax with drying oil, resin, mineral oil, cellulose, rubber derivatives, and the like.

Representative examples of wax include microcrystalline wax, carnauba wax, paraffin wax, and the like. Furthermore, various waxes are used, such as Fischer-Tropsch wax, various low molecular weight polyethylenes, wood wax, beeswax, spermaceti wax, privet wax, wool wax, shellac wax, candelilla wax, petrolatum, assorted waxes, fatty acid esters, and fatty acid amides. It will be done.

Furthermore, a thermally conductive substance can be blended into the hot-melt ink layer in order to provide the hot-melt ink layer with good thermal conductivity and melt transferability. Examples of this substance include carbonaceous substances such as carbon black, aluminum, copper, tin oxide, and molybdenum dioxide.

In the present invention, the ink layer 2 is replaced by a heat-melting release layer 3.
A plurality of layers are formed in order from a layer with a high softening point to a layer with a low softening point through the process. For example, the first layer 2. For example, when forming with ink having a softening point of 83°C, the second layer 22
are formed with an ink having a softening point lower by about 1 to 10 degrees Celsius than that, for example, an ink with a softening point of 75 degrees Celsius, and similarly the third layer 23, the fourth layer 24, the fifth layer 2s...the first layer 2n and ink layers with lower softening points are sequentially laminated. Generally, the number n of such ink layers is 2 or more and 9 or less; if it is 10 or more layers, the thickness of the entire ink layer is too large, and heat transfer to the outermost surface zn is not sufficient. .

The softening point of each ink layer can be easily adjusted by selecting the type of wax, combining different types of wax, and using additives such as resins.

When forming each of the above ink layers, a heat-melting release layer 3 is formed between each of the layers. These release layers are
The layer should have a lower softening point than the ink layers on both sides, and each release layer should have a softening point of 3. It is preferable that the softening point is lower as it approaches the surface, such as 〉3z＞3*... That is,
The farther the layer is from the thermal head 6, the less heat transfers, so it is preferable to use a release layer with a lower softening point.If it is the other way around, the release layer will not separate each layer and the entire layer will be removed at once. There is a risk of thermal transfer.

The release layer as described above is preferably formed from the various waxes mentioned above, and their softening points can be adjusted in the same way as the softening point of the ink layer.

As a method for directly or indirectly forming the plurality of heat-melt ink layers 2 and release layer 3 on the base film 1, in addition to applying a hot-melt coating liquid, adding a solvent and melting it by heating or melting it at room temperature can be used. Examples include methods of applying a coating liquid using gravure coating, gravure reverse coating, roll coating, and many other methods. The thickness of the ink layer and release layer to be formed should be determined so as to balance the required optical density and thermal sensitivity, and both should be in the range of 0.1 to 10μ.
m, preferably in the range 1 to 5 μm.

The above is the basic structure of the thermal transfer sheet of the present invention. Furthermore, in a preferred embodiment of the present invention, a surface layer 5 is provided on the surface of the uppermost ink layer, and an anti-sticking layer 4 is provided on the back surface of the base film. be able to. Furthermore, a layer having fine irregularities may be provided on the surface of the base film so as to obtain matte printing.

In the present invention, the surface layer 5 formed on the ink layer is
It forms a part of the top layer of the transfer film, and forms the surface that contacts the transfer paper to seal the printed area of the transfer paper during transfer, and also prevents background smearing, as well as to protect the ink layer from the transfer paper. It has the function of improving adhesion to.

The above surface layer may be formed using a wax melt, an organic solvent solution, or an aqueous dispersion, and may further include a thermoplastic resin, extender pigment, or other arbitrary additives as necessary. good.

The wax used to form the surface layer is the same as the wax used in the hot-melt ink layer described above. The thickness of this layer is preferably 0.1 μm or more and less than 5 μm.

If the thickness is less than 0.1, there is a risk that the transfer paper and the ink layer will rub against each other, causing scumming.

Note that during the second thermal transfer, part of the surface layer is chipped and the release layer 32 is exposed in that part.
2 acts as a surface layer, and there is no need to worry about background stains on the transfer paper due to that part.

When a heat-resistant material is used for the base film, it is preferable to provide a layer 3 on the surface in contact with the thermal head to prevent sticking of the thermal head. The basic components of the anti-sticking layer 4 are a heat-resistant resin and a substance that functions as a heat release agent or a lubricant. Heat-resistant resins include synthetic resins with a glass transition point of 60°C or higher, or thermoplastic resins having one OH group or Coo), and a compound having two or more amino groups, or a diisocyanate or triisocyanate. Those that have undergone crosslinking and curing are preferred.

Thermal mold release agents or lubricants include waxes, amides, esters, and salts of higher fatty acids that melt when heated, and powders of organic substances such as fluororesin and powders of inorganic substances. Some are useful while remaining solid.

By providing such an anti-sticking layer 4, it is possible to perform thermal printing without causing sticking even on a thermal transfer sheet based on a plastic film that is sensitive to heat. Benefits such as ease of use can be taken advantage of.

It goes without saying that the present invention can be applied to heat-sensitive transfer sheets for color printing, and therefore multi-colored heat-sensitive transfer sheets are also included within the scope of the present invention.

(Effect) When forming multiple ink layers on a base film, these multiple ink layers are laminated in order from one with a high softening point to one with a low softening point, and between these ink layers, By laminating a release layer with a lower softening point than the ink layer, clear layer separation occurs at the release layer with a lower softening point during transfer, and the transfer is transferred to the receiving paper. Clear and reliable thermal transfer is possible. Further, a thermal transfer device using such a thermal transfer sheet of the present invention,
This is a device that can vary the energy applied to the thermal head, and it is preferable to adjust the energy applied depending on the number of thermal transfers.

(Example) Hereinafter, the present invention will be explained in more detail with reference to Examples.

In addition, unless otherwise specified, the words "part" or "%" in the text refer to weights.
fl standard.

Example 1 Heat-melt ink layered inks A and B and release layer ink A, X and B were formed in this order on one side of polyethylene terephthalate having a thickness of 3.5 μm by a conventional method to obtain a thermal transfer sheet of the present invention.

A (softening point: 84°C) Carbon black (Diablack G, manufactured by Mitsubishi Kasei)
1 part ethylene/vinyl acetate copolymer (EVA Flex 31O1 manufactured by Mitsui Polychemicals) 1 part carnauba wax
2-part λヱ1 (softening point 75℃) Carbon black (Diablack G, manufactured by Mitsubishi Kasei)
3 parts ethylene/vinyl acetate copolymer (EVA Flex 31O1 manufactured by Mitsui Polychemicals) 1 part microcrystalline wax (HIMIC 2065, manufactured by Nippon Seiro) 10 parts Emago (softening point 65°C) Candelilla wax alone The above thermal transfer Thermal transfer was performed twice using a commercially available thermal head using plain paper as the transfer paper.

The energy of the first thermal head is 0.8W/dot, and the energy of the second thermal head is 1.0W/dot.
It was a dot. Good images were formed in all cases.

Example 2 Inks C and D for hot-melt ink layers and ink Y for release layers having the following compositions were prepared, and these inks had dry film thicknesses of 2.0 μm, 1.0 μm, and 2 μm, respectively. The thermal transfer sheet of the present invention was obtained by forming C, Y and D in this order on one side of polyethylene terephthalate having a thickness of 3.5 μm by a conventional method.

Engineering soil (softening point 96℃) Carbon black (Diablack G, manufactured by Mitsubishi Kasei)
1 part ethylene/vinyl acetate copolymer (EVA Flex 31O1 manufactured by Mitsui Polychemicals) 1 part microcrystalline wax (Himic 2095, manufactured by Nippon Seiro) 2
Part Ink B (softening point 68℃) Carbon black (Diablack G1 manufactured by Mitsubishi Kasei)
3 parts ethylene/vinyl acetate copolymer (EV^flex 31O1 manufactured by Mitsui Polychemicals) 1 part butterfin wax (paraffin 155)
F, made by Nippon Seiro Co., Ltd.) 10 parts (softening point: 66°C) Candelilla wax alone Using the above thermal transfer sheet, using plain paper as the transfer paper, and using a commercially available thermal head, transfer was performed twice. Thermal transfer was performed.

The energy of the first thermal head is 0.8W/dot, and the energy of the second thermal head is 1.0W/dot.
It was a dot. Good images were formed in all cases.

Example 3 Inks E and FG for hot-melt ink layers and inks Y and Z for release layers having the following compositions were prepared, and these inks had film thicknesses of 2.0 μm, 1.0 μm, and 2 μm when dried, respectively.
Repeat E, Y, F, Z and G in the order of
The thermal transfer sheet of the present invention was obtained by forming it on one side of polyethylene terephthalate having a thickness of 3.5 μm by a conventional method.

Ink E (softening point 84℃) Carbon black (Diablack G, manufactured by Mitsubishi Kasei)
1 part ethylene/vinyl acetate copolymer (EV^Flex 31O1 manufactured by Mitsui Polychemicals) 1 part carnauba wax
2 parts m Saturday (softening point 68℃) Carbon black (Diablack G, manufactured by Mitsubishi Kasei)
3 parts ethylene/vinyl acetate copolymer (EV^flex 31O1 manufactured by Mitsui Polychemicals) 1 part butterfin wax (paraffin 155)
F, made by Nippon Seiro) io part L Shieya (softening point 64℃) Carbon black (Diablack G, made by Sanichigo Kasei)
3 parts ethylene/vinyl acetate copolymer (EVA Flex 310, manufactured by Mitsui Polychemicals) 1 part butterfin wax (paraffin 15
Kano, manufactured by Nippon Seiro Co., Ltd.) 10 parts m soil Plain paper was used as the paper, and thermal transfer was performed three times using a commercially available thermal head.

The energy of the first thermal head is 0.5W/dot, and the energy of the second thermal head is 9.7W/dot.
Dot, the energy of the third thermal head is 1.0
W/dot. Good images were formed in all cases.

[Brief explanation of the drawing]

FIG. 1 is a diagram schematically showing a part of a cross section of the heat-sensitive transfer sheet of the present invention, and FIG. 2 is a diagram schematically showing a method of using the heat-sensitive transfer sheet of the present invention. 1: Base film 2: Hot melt ink layer 3: Peeling layer 4: Anti-sticking layer 5: Surface layer 6: Thermal head 7: Transfer paper Patent applicant Dai Nippon Printing Co., Ltd. Agent Patent attorney Yoshi 1) Katsuhiro

Claims (6)

[Claims] (1) A plurality of heat-melt ink layers with different softening temperatures are laminated on one side of the base film via a heat-melt release layer with a lower softening point than these ink layers, and these multiple A heat-sensitive transfer sheet characterized in that the ink layer has a softening point that gradually decreases as the distance from the base film increases. (2) The difference in the softening temperature of the heat-fusible ink layer is 1°C to 20°C.
℃ range, according to claim (1). (3) The heat-sensitive transfer sheet according to claim (1), wherein the total number of heat-melting ink layers is 2 to 9. (4) The thermal transfer sheet according to claim (1), which has an anti-sticking layer on the back surface of the base film. (5) The heat-sensitive transfer sheet according to claim (1), which has a surface layer on the outermost surface of the heat-melting ink layer. (6) The heat-sensitive transfer sheet according to claim (1), wherein a fine uneven layer is provided on the heat-melt ink side between the base film and the heat-melt ink layer.