JPH0478113B2 - - Google Patents

Description

[Detailed description of the invention]

"Industrial Application Field" The present invention relates to a thermal transfer recording medium used for recording on a recording medium by heating and melting or sublimating ink. "Prior Art" When recording an image corresponding to a predetermined digital image signal on a recording medium, for example, plain paper,
Recording methods using thermal transfer recording media such as ink donor films are widely employed. Among these, the thermal head transfer method uses a thermal head in which a large number of heating elements are arranged in a row. In this method, a base film coated with ink is placed with its ink side facing recording paper (plain paper), and a thermal head selectively applies heat pulses from the back of the base film to remove ink from that area. It is transferred onto recording paper by melting or sublimating it (Japanese Unexamined Patent Application Publication No. 1989-1999).
84735, etc.). On the other hand, the energization transfer method is a method in which a needle electrode is brought into contact with a base film coated with ink, and the ink is selectively energized to heat the ink with Joule heat. This method requires the ink layer and the base film to be electrically conductive. In order to impart conductivity to the base film, methods are used such as dispersing metal in a resin and forming it into a film (ribbon), or using a high-resistance conductive polymer resin. A material with good conductivity is mixed into the ink layer (Journal of the Institute of Image Electronics Engineers, Vol. 11, No. 1, 1982). Although it is a similar method, instead of heating the ink by passing a current directly through it, the ink layer is coated on the base film through a heating resistor layer, and the ink is heated by passing current through the heating resistor layer. A method has been proposed to do this (Japanese Patent Application Laid-Open No. 56-93585, etc.). Hereinafter, this will be referred to as a thermal transfer printing method. This method will be explained using FIG. 4. In the figure, a thermal transfer recording medium 10 has a structure in which a heat generating resistor layer 4, a conductive layer 5, and an ink layer 6 are laminated in this order on a base film 3.
This base film 3 is given a predetermined electrical conductivity. On the back side of this thermal transfer recording medium 10,
The needle electrode 1 and the return electrode 2 are brought into contact. here,
A large number of needle electrodes 1 are arranged in a line in a direction perpendicular to the plane of this paper, and electric pulses are selectively applied to some of them in accordance with the image signal. The current flows as shown by the dashed-dotted arrow 11. The portion of the heating resistor layer 4 indicated by the arrow 12 generates heat. This heat melts and softens a portion 8 of the ink layer 6, and the ink 8 is transferred to the recording paper 7. "Problems to be Solved by the Invention" The above-mentioned conventional techniques each have the following problems. First, in the thermal head transfer method, heat is transferred from the thermal head to the ink layer via the base film, so there is a time lag in recording (time constant of about 1 msec) due to the time required for heat conduction, and the printing speed decreases. The problem is that it is slow. Furthermore, it is necessary to use inks that transfer less thermal energy and have lower melting points. Therefore, the degree of freedom in selecting the ink material is small, and transfer controllability is not good. For this reason, it is difficult to modulate the density of recording dots, and there is also the drawback that only wax-based materials can be used as ink materials. Furthermore, the electric transfer method has the disadvantage that it is difficult to produce color images because the conductive material added to the ink makes it difficult to control the color tone. Furthermore, in addition to power loss due to electrical resistance within the base film, loss occurs due to current spread, resulting in poor power efficiency and low positional accuracy of recording dots. Furthermore, if a conductive material is added to the base film, its mechanical properties will also be degraded. On the other hand, thermal transfer printing does not require the ink to be electrically conductive and has a high degree of freedom in selecting ink materials, but has the disadvantages of large losses due to current spread and low positioning accuracy of recording dots. is no different from the current transfer method. Further, as is clear from FIG. 4, the base film 3 is connected to the heating resistor layer 4.
Since it is necessary to have a sufficiently high resistance, the contact resistance with the needle electrode 1 etc. inevitably becomes high. Moreover, since the current reaches the return electrode 2 by following the same path as the needle electrode 1, base film 3, heating resistor layer 4, and conductive layer 5,
There are two contact points in the current path, which causes a large loss of electrical energy. The present invention has been made focusing on the above points,
An object of the present invention is to provide a thermal transfer recording medium that can perform efficient and highly accurate transfer. "Means for Solving the Problems" The thermal transfer recording medium of the present invention is produced by heating an ink containing a thermoplastic polymer material as a main component on a support.
In the case of transferring onto a recording medium, the support includes an anisotropic conductive layer whose conductivity in the thickness direction is selected to be at least 10 times the conductivity in the width direction, and a volumetric conductive layer laminated in order on the anisotropic conductive layer. Specific resistance is 10 ^-2 per unit area
It is composed of a heating resistor layer having a resistance of Ω·cm or more and 10 ⁴ Ω·cm or less, a return electrode layer having a volume resistivity of 1/10 or less of this heating resistor layer, and an ink peeling layer that carries ink. It is characterized by: "Function" In the above-described thermal transfer recording medium, the anisotropic conductive layer is provided to allow current to flow in the thickness direction from the needle electrode in contact with the heat generating resistor layer with low loss. The heating resistor layer is a layer that generates heat due to Joule heat generated by this current, and heats the ink to transfer the ink. The return electrode layer serves as an electrode that diffuses and refluxes the current that has flowed into the heating resistor layer. Further, the ink release layer is a layer whose critical surface tension is adjusted so that ink transfer can be performed satisfactorily even at low energy. With such a configuration, high-quality recording can be performed with high efficiency and high speed. "Example" (Basic Configuration) FIG. 1 is a longitudinal sectional view showing the basic configuration of the thermal transfer recording medium of the present invention. This thermal transfer recording medium has an ink layer 26 formed on a support 20. This support 20
includes an anisotropic conductive layer 23 whose conductivity in the thickness direction (direction of arrow X) is higher than conductivity in the width direction (direction of arrow Y), a heating resistor layer 24, and a return electrode layer 25.
and an ink release layer 28. It is preferable that the conductivity in the thickness direction of the anisotropic conductive layer 23 is about 10 times or more than the conductivity in the width direction, and for example, as shown in FIG. A conductive linear body 23a such as a nickel wire is molded and fixed with an elastic resin 23b such as a silicone elastomer. The resistance value of this anisotropic conductive layer 23 in the thickness direction is
Select 200Ω or less, preferably 20Ω or less. The heating resistor layer 24 is made of a material having heat resistance of 200° C. or higher, such as ceramic such as TaN, and its volume resistivity is 10 ^-2 Ω·cm to 10 ⁴ Ω·cm per unit cross-sectional area. The range is preferably selected from 10 Ω·cm to 10 ³ Ω·cm. Also,
Its thickness is 3000 Å in terms of the mechanical properties of the support.
It is preferable to select the range from 20 μm to 20 μm. If the thickness of the heat generating resistor layer 24 is selected within such a range, and its volume resistivity exceeds the above range, high voltage drive will be required to supply the current necessary for heat generation, causing damage to circuits and other parts. Reliability decreases in terms of voltage resistance, etc. On the other hand, when the volume resistivity falls below the above range, it becomes necessary to supply a large current to generate heat, leading to an increase in cost due to an increase in the size of the circuit. Next, the return electrode layer 25 is formed by vapor deposition of a conductive metal, and its volume resistivity is 5×10 ^-1 times or less that of the heating resistor layer 24, preferably 1×
Select a material with a heat resistance of 10 ^-1 times or less and a heat resistance of 200℃ or higher. This return path electrode layer 25 is grounded through an electrode (not shown) or connected to an electrode with a constant bias potential. The ink release layer 28 is formed of a material having a lower critical surface tension (γc) than the critical surface tension (γc) of the surface of the transfer material such as recording paper so that the ink can be easily transferred when heated. It is preferable that the film be an extremely thin film. Its thickness is 10μm or less,
Preferably, it is selected to be 1 μm or less. The ink layer 26 is colored by mixing or dissolving a coloring material based on a polymer substance having a glass transition temperature of 130° C. or less. (Operation) FIG. 3 schematically shows a recording apparatus that performs recording using the thermal transfer recording medium as described above. The thermal transfer recording medium 30 is conveyed from a supply reel 31 toward a take-up reel 32 . Recording paper 3
3 is superimposed on this thermal transfer recording medium 30 and is conveyed between a pair of conveyance rollers 34. A recording head 35 in which needle electrodes 21 (FIG. 1) are arranged in a row is located between a pair of conveyance rollers 34.
The thermal transfer recording medium 3 cooperates with the back elastic roller 36.
0 and recording paper 33 are sandwiched between them, and an electric pulse for recording is applied. Here, as shown in FIG. 1, when the needle electrode 21 is brought into pressure contact with the anisotropic conductive layer 23 and an electric pulse is applied, the signal current is transmitted between the needle electrode 21, the linear body 23, and the anisotropic conductive layer 23.
a, it flows through the heating resistor layer 24 and the return electrode layer 25 as shown by the dashed-dotted arrow. The electrical resistance of the anisotropic conductive layer 23 in the X direction is sufficiently low, and the current widely diffuses in the return electrode layer 25, so the electrical resistance is also low here, and most of the electrical energy supplied from the needle electrode 21 is It is converted into thermal energy in the heating resistor layer 24. This heat travels through the return electrode layer 25 and the ink peeling layer 28 and reaches the ink layer 26 . In this way, the ink in the ink layer 26 is heated and melted and transferred to recording paper or the like. At this time, since the return electrode layer 25 and the ink peeling layer 28 are made sufficiently thin,
Heat transfer rate is fast and energy loss is low. By configuring the thermal transfer recording medium of the present invention as described above, the energy effectively used for recording is 15% or more of the input energy, and recording can be performed with extremely high efficiency. Therefore, the energy supplied for recording may be less than 500 erg per dot, and high-speed recording of less than 500 μsec/dot is possible. Further, by providing the ink peeling layer 28, the ink transfer efficiency is improved, and the amount of dot transfer can be changed by modulating the input energy, making it possible to perform so-called multi-gradation recording. More specific examples of the present invention will be described below. (Specific Examples) Each part of the thermal transfer recording medium shown in FIG. 1 was manufactured as follows. Anisotropic conductive layer 23 Ni wires with a diameter of 15 μm and plated with gold vapor deposition are arranged in parallel at a density such that at least one wire exists in an area of 40 μm x 40 μm, and fixed in a mold with room temperature curing silicone elastomer. An anisotropic conductive layer was created. Its surface is 300Å
Precision finish polishing was performed to achieve the above surface accuracy. Its thickness is 2 mm, and the resistance value per unit area in the thickness direction (X direction in Figure 1) is 0.7Ω.
The resistance value in the plane direction (Y direction in FIG. 1) was 10 ¹⁴ Ω or more. The anisotropic conductive layer obtained in the heating resistor layer 24 is thoroughly washed and dried, and then argon gas is blown into the vacuum system at a vacuum level of 2 x 10 ^-6 Torr to achieve a vacuum level of 3 x 10 ^-3 Torr. After introduction, high frequency sputtering method
A TaN target containing 20% by weight of SiO ₂ was sputtered to a resistance of 80Ω/10 ^-2 mm ² ,
A heat generating layer with a thickness of 2500 Å was formed. Cr was added to the obtained return electrode layer 25 by electron beam vacuum evaporation at an ultimate vacuum of 1.5×10 ^-6 Torr.
A return electrode layer was obtained by depositing a film of 500 Å and a Cu film of 2000 Å. Ink release layer 28 A polyfluoroethylene resin film having a thickness of 3 μm was sintered on the return electrode layer to form an ink release layer. Its critical surface tension was 20 dyne/cm. Ink Layer 26 On the above ink release layer, a thermoplastic magenta ink layer having a thickness of 10 μm was formed by mixing 15 weight percent of strontium salt and pigment from Resole Red into a polyester resin (Vylon 200 manufactured by Toyobo Co., Ltd.). The thermal transfer recording medium thus obtained was set in an apparatus as shown in FIG. 3, and recording was carried out using a line head in which needle electrodes each having a diameter of 90 μm were arranged at a density of 8 needles/mm. The electric pulse for recording is 15V,
There are four types: 40V, 80V, and 150V, all with different widths.
A rectangular pulse of 150 μsec was used. Plain paper for copying was used as the recording paper, and recording was performed by sandwiching the thermal transfer recording medium and the recording paper by pressing the line head with a pressure of 800 g/cm ² against an elastic back roller with a rubber hardness of 45. . In the return electrode layer 25,
The electrodes were connected to continuously apply a rectangular pulse of 30 V with a width of 120 μsec. In this way, thermal transfer recording was performed in accordance with the image signal, and transferred dots (recorded dots) were evaluated.

[Table] Comparative Example 1 A thermal transfer recording medium having the same structure as in the above example but excluding only the ink release layer was manufactured, and the same recording was performed to evaluate the transferred dots. At this time, the Cu surface of the return electrode layer (the surface in contact with the ink layer)
The critical surface tension of was 62 dyne/cm.

[Table] Comparing these results with Table 1, the effect of the ink release layer on ink transfer can be clearly recognized. Comparative Example 2 A heat transfer resistor layer having a structure similar to that of the above example was manufactured by sputtering only SiO ₂ to a thickness of 200 Å, and was evaluated in the same manner as above.

[Table] Since SiO ₂ is an insulator, the reason why recording was possible when the electric pulse width was made sufficiently larger than in the example is considered to be due to heat generation in the return electrode layer. Comparative Example 3 Anisotropic conductive layer 2 with the same configuration as the above example
As an alternative to No. 3, a silicone elastomer in which 30% by weight of carbon was dispersed to impart electrical conductivity was used. Its thickness was 2 mm, and the resistance value in the thickness direction was 110Ω.

[Table] In this case, the energy loss was significant, and this is thought to be the result of insufficient current being supplied to the heating resistor layer to heat the ink. "Effects of the Invention" The thermal transfer recording medium of the present invention as described above has the following effects. (1) High-speed printing is possible The ink layer is close to the heat-generating resistor layer, so heat transfer is fast, and the time constant during printing is small at 200 μsec or less, so high-speed printing of 100 cpm is possible if you convert it to a line head. It is. (2) High quality images can be obtained. In the case of the thermal transfer recording medium of the present invention, the ink material need only be thermoplastic, and the degree of freedom in selection is extremely high. For example, when selecting and blending a coloring material into a transparent polymeric material, it is possible to select the coloring material (pigment or dye) from a wide range depending on the color tone, and also because the coloring material is surrounded by the polymeric material. Therefore, the coloring material is less likely to deteriorate or decompose due to direct irradiation with ultraviolet light or contact with oxygen. Therefore, the color tone and fastness of the coloring material can be made to the same level as printing. (3) High gradation can be obtained. Since the responsiveness to the input signal is good, the amount of transferred ink can be adjusted by modulating the intensity of the input signal. Therefore, it is possible to express the density of each dot in three or more levels, rather than expressing the gradation using a so-called dot matrix pattern method. Therefore, it is possible to express halftones in 8 to 16 levels while maintaining a high resolution of 6 to 8 lines/mm. Of course, full color gradation expression is also possible. (4) Energy saving can be achieved. As mentioned above, since the heating resistor layer and the ink layer are close to each other, there is little energy loss due to thermal diffusion. In addition, the electrical resistance of the current path that guides the current to the heating resistor layer is low, and energy loss due to this is also small. Of course, since fixing processing and the like are not required, there is no wasted energy consumption. From this, when the recording density is 8 dots/mm, 1
It is economical to be able to record with energy of 100 to 700 erg per dot. (5) High reliability. The amount of heat generated can be controlled by managing the resistance value of the heating resistor layer, and if a heat-resistant material such as ceramic is used for this heating resistor layer, the thickness can be easily controlled to several tens of angstroms (Å). This can be manufactured. Moreover, the humidity is 10-90%
(Rh), the process (recording operation) operates stably in the temperature range of 5 to 30°C, and high reliability can be obtained. Therefore, there is no need for humidity control during handling of powder as in laser printers and electrostatic recording methods, temperature control for stabilizing ink viscosity as in inkjet methods, and maintenance management is easy.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the thermal transfer recording medium of the present invention, FIG. 2 is a partially cutaway perspective view of its anisotropic conductive layer, and FIG.
The figure is a schematic diagram of a recording apparatus using the thermal transfer recording medium of the present invention, and FIG. 4 is a longitudinal cross-sectional view of a conventional thermal transfer recording medium. 20...Support, 23...Anisotropic conductive layer, 23
a... Linear body, 24... Heat generating resistor layer, 25...
Return electrode layer, 26... ink layer, 28... ink release layer.

Claims (1)

[Claims] 1 In a device in which ink containing a thermoplastic polymer material as a main component on a support is heated and transferred onto a recording medium, the support has a conductivity in the thickness direction that is 10 times higher than the conductivity in the width direction. An anisotropic conductive layer selected to have a volume resistivity of 10 ^-2 Ω・cm or more per unit cross-sectional area, 10 ⁴ Ω・cm or more
The following heating resistor layer, a return electrode layer having a volume resistivity of 1/10 or less of this heating resistor layer,
A thermal transfer recording medium comprising an ink release layer supporting ink.