JPH01113285A - Thermal transfer sheet - Google Patents

Abstract

PURPOSE:To obtain a thermal transfer sheet capable of being used for thermal transfer a plurality of times through using a wax or the like and without need for a special means, by alternately providing a plurality of heat-fusible ink layers differing in softening temperature on one side of a base film. CONSTITUTION:A plurality of ink layers 2, namely, higher softening point layers and lower softening point layers, are alternately provided on a base film 1. In the first run of printing, the entire body of the ink layers 2 is heated from the back side by a thermal head 5. In this case, since the ink layers 21, 23 and 25 have relatively higher softening points whereas the ink layers 22 and 24 have relatively lower softening points, the layer 25 adhered to a transfer recording paper 6 is released at the layer 24. The interface between the layer 25 and the layer 24 is closer to the thermal head 5 than does the interface between the layer 24 and the layer 23, and is therefore softened to a lower viscosity, so that the layer 24 is thermally transferred to the paper 6 together with the layer 25. In the second run of printing, the layers 23 and 22 are thermally transferred in the same manner as above. In the third run of printing, the layer 21d is thermally 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 10 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 and 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 micrometers, 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, the present invention is a heat-sensitive transfer sheet characterized in that a plurality of heat-melting ink layers having different softening temperatures are alternately laminated on one surface of a base film.

(Function) When forming multiple ink layers on the base film, by alternately laminating layers with a lower softening point and layers with a higher softening point, it is possible to Clear layer separation occurs at the layer with a low softening point, and the ink layer with a low softening point and the ink layer with a high softening point are transferred as a pair 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. ．． , 2□, 23-2n force%, and is characterized in that the ink layer 2 of these a numbers is formed by alternately laminating layers with a high softening point and layers with a low softening point. Furthermore, there is an anti-sticking layer 3 on the other side of the base film 1, and a surface layer (on the ink layer 2n).
A closure layer) 4 may be formed.

For example, an example where the total number of ink layers is 5 (n=5) (
To explain multiple thermal transfers using FIG. 1), in the first printing, the entire layer 2 is heated by the heating of the thermal head 5 from the back side, as shown in the second drawing.
In this case, layers 21, 23 and 25 are ink layers with relatively high softening points, while layers 22 and 24 are ink layers with relatively low softening points.
The 25 layers adhered (via) peel off at layer 24.

In this case, looking at the thickness direction of 24 layers, 25 layers and 2
Since the interface between the 24th layer and the 23rd layer is closer to the thermal head 5 than the interface with the 4th layer, the 24th layer softens to a lower viscosity, and the 24th layer softens to a lower viscosity.
The layers are thermally transferred to the receiving paper 6 along with 25 layers.

In the second printing, 23 layers and 22 layers are printed in the same way as above.
23 layers are thermally transferred in the third printing.

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 l 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 such as Fischer-Tropsch wax, various low molecular weight polyethylenes, wood wax, beeswax, spermaceti wax, privet wax, η hair wax, shellac wax, candelilla wax, petrolatum, partially modified waxes, fatty acid esters, fatty acid amides, etc. used.

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 laminated into a plurality of layers. For example, the first layer 21 may have a softening point of 66°C.
In the case of forming the second layer 22 with an ink having a softening point lower by about 1 to 10 degrees Celsius, for example, an ink with a softening point of 64 degrees Celsius, the third layer 23 is formed in the same way.
, fourth layer 24, fifth layer 25, . . . , ink layers having different softening points are alternately laminated with the 0th layer 2n. Although these ink layers can be formed from different inks, it is preferable to form layers alternately using two types of ink having different softening points, which is economical. Number n of such ink layers
is generally 3 or more and 9 or less, and 10
The thickness of the entire ink layer is too large, and the outermost surface 2n
There is no longer sufficient heat transfer.

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.

Further, the plurality of ink layers as described above are arranged so that both the ink layer with a relatively low softening point and the ink layer with a relatively high softening point are higher as they are closer to the base film and lower as they are closer to the surface. is also preferable. In other words, the farther the layer is from the thermal head 5, the less heat transfers, so it is preferable to use an ink layer with a lower softening point.If it is the other way around, the ink layer will not be peeled off layer by layer, and the entire layer will be There is a risk of thermal transfer at one time.

As a method for directly or indirectly forming the plurality of heat-melting ink layers 2 on the base film 1, in addition to applying a heat-melting type coating liquid, the TLT5 liquid in which a solvent is added and melted by heating or melting at room temperature is used. Examples include methods of coating by gravure coating, gravure reverse coating, roll coating, and many other methods. The thickness of the ink layer formed should be determined to balance the required optical density and thermal sensitivity, and is preferably in the range from 0.1 to 10 μm! The range is from 5 μm to 5 μm.

The above is the basic structure of the thermal transfer sheet of the present invention. In a preferred embodiment of the present invention, a surface layer 4 is further provided on the surface of the uppermost ink layer, and an anti-sticking layer 3 is provided on the back surface of the base film. be able to.

In the present invention, the surface layer 4 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.

During the second thermal transfer, part of the surface layer is chipped, and the ink layer 23 is exposed in that part, but since the chipped part is a recess, the background stain of the transfer paper due to that part may occur. There's no need to worry.

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 3 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 OH or COOH groups, and a compound having two or more amino groups, or diisocyanate or triisocyanate added to slightly crosslink and cure. Preferably, those that cause

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 and inorganic substances such as fluororesins. There are some things that are useful as solids, such as.

By providing such an anti-sticking layer 3, 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 the base film, by alternately laminating layers with a lower softening point and layers with a higher softening point, it is possible to There is clear delamination at the layer with a low softening point, and the ink layer with a low softening point and the ink layer with a high softening point are transferred as a pair to the receiving paper. Clear and reliable thermal transfer is possible. Further, the thermal transfer device using such a thermal transfer sheet of the present invention is a device in which the applied energy of the thermal head can be varied, and the applied energy can be changed depending on the number of thermal transfers. ! It is better to do one verse.

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

In the text, parts or percentages are based on weight unless otherwise specified.

Example 1 Heat-melt ink layered inks A and B having the following compositions were prepared, and each of these inks was mixed with one side of polyethylene terephthalate having a thickness of 3.5 μm so that the dry film thickness was 2.0 μm. The first layer, third layer and v
A second layer and a fourth layer were formed using the IS layer and ink B by a conventional method to obtain a thermal transfer sheet of the present invention.

LλヱA (softening point 84℃) Carbon black (Diablack G, manufactured by Mitsubishi Kasei)
1 part ethylene/vinyl acetate copolymer ([VA Flex 310, manufactured by Mikata Polychemical) 1 part carnauba wax
2 parts ff Hiki 1 (softening point 64℃) Carbon black (Diablack G, manufactured by Mitsubishi Kasei)
3 parts ethylene/vinyl acetate copolymer (EVA Flex 31O1 manufactured by Mitsui Polychemicals) 1 part paraffin wax (paraffin 15
0F, manufactured by Nippon Seiro Co., Ltd.) 10 copies Using the above thermal transfer sheet, plain paper was used as the transfer paper, and thermal transfer was performed three times using a commercially available thermal head.

The energy of the first thermal head is 0.8W/dot, and the energy of the second thermal head is 0.7W/dot.
Dot, the energy of the third thermal head is 0.6
W/dot. Good images were formed in all cases.

Example 2 Heat-melt ink elbow inks C and D having the following compositions were prepared, and each of these inks was mixed with one side of polyethylene terephthalate having a thickness of 3.5 μm so that the dry film thickness was 3.0 μm. A first layer and a third layer using ink C and a second layer using ink D were formed on the surface by a conventional method to obtain a thermal transfer sheet of the present invention.

Funomako (softening point 68℃) Carbon black (Diablack G, manufactured by Mitsubishi Kasei)
1 part ethylene/vinyl acetate copolymer (EVA Flex 31O1 manufactured by Mitsui Polychemicals) 1 part paraffin wax (paraffin 15
5F, made by Nippon Seiro) 2 parts Otsu1 Dodan (softening point 65℃) Carbon black (Diablack G, made by Mitsubishi Kasei)
3 parts ethylene/vinyl acetate copolymer (EV^Flex 31O5 manufactured by Mitsui Polychemicals) 1 part carnauba wax
2 parts paraffin wax (paraffin 15 leaves, manufactured by Nippon Seiro Co., Ltd.) 1 part Using the above thermal transfer sheet, plain paper was used as the transfer paper, and thermal transfer was performed twice using a commercially available thermal head.

The energy of the first thermal head is 0.8W/dot, and the energy of the second thermal head is 0.7W/dot.
It was a dot. Good images were formed in all cases.

Example 3 Heat-melt ink elbow inks E and F having the following compositions were prepared, and each of these inks was mixed with one side of polyethylene terephthalate having a thickness of 3.5 μm so that the dry film thickness was 1.0 μm. 1st layer, 3rd layer, and 5th layer with ink F on the surface of
layer and 7th layer, 2nd layer, 4th layer and 6th layer with ink B.
The layers were formed by a conventional method to obtain a thermal transfer sheet of the present invention.

mEgo (softening point 74℃) Carbon black (Diablack G, manufactured by Mitsubishi Kasei)
1 part ethylene/vinyl acetate copolymer (EVA Flex 31O1 made by Mitsui Polychemicals) 1 part microcrystalline wax (made by Himic 2065.1 layer genuine rust wax) 3
Part EEV (softening point 64℃) Carbon black (Diablack G, manufactured by Mitsubishi Kasei)
3 parts ethylene/vinyl acetate copolymer (EV^Flex 310, manufactured by Mikata Polychemical) 1 part paraffin wax (Paraffin 15
0F, manufactured by Nippon Seiro Co., Ltd.) 8 copies Using the above thermal transfer sheet, plain paper was used as the transfer paper, and thermal transfer was performed four times using a commercially available thermal head.

The energy of the first thermal head is 1.0W/dot, and the energy of the second thermal head is 1.0W/dot.
Dot, the energy of the third thermage head is 0.
The energy of the fourth thermal head was 8 W/dot, and the energy of the fourth thermal head was 0.6 W/dot. Good images were formed in all cases.

[Brief explanation of the drawing]

FIG. 4 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. ! =Base film 2: Hot-melt ink layer 3: Anti-sticking layer 4: Surface layer 5: Thermal head 6: Transfer paper Patent applicant Dai Nippon Printing Co., Ltd. Representative Patent attorney Yoshi 1) Katsuhiro Figure 1 Figure 2 figure

Claims (6)

[Claims] (1) A heat-sensitive transfer sheet comprising a plurality of heat-melting ink layers having different softening temperatures alternately laminated on one side of a base film. (2) The thermal transfer sheet according to claim (1), wherein the difference in softening temperature is in the range of 1°C to 20°C. (3) The heat-sensitive transfer sheet according to claim (1), wherein the total number of heat-melting ink layers is 3 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 thermal transfer sheet according to claim (1), wherein a layer with unevenness is provided on the surface of the base film so as to obtain matte printing.