JPS6394888A - Thermal transfer recording medium - Google Patents

Abstract

PURPOSE:To enable a good-efficiency and high-accuracy transfer, by a method wherein a substrate is provided with an ink separating layer on the ink holding side thereof and the critical surface tension of the ink holding surface of the ink separating layer is selected to be less than a specific value. CONSTITUTION:An ink layer 26 is formed on a substrate 20 consisting of an anisotropic conductive layer 23 having an electrical conductivity in the thickness's direction higher than that in the width's direction, a heating resistor layer 24, a return electrode layer 25, and an ink separating layer 28. The ink separating layer 28, which is a very thin film made of a material having a critical surface tension lower than that of the surface of a transfer material such as a recording paper, has the critical surface tension of the ink holding surface selected to be 38dyne/cm or below. For example, a plain paper of 40-50dyne/cm surface energy or an OHP sheet of 40-45dyne/cm is used as the transfer material, thus having a difference of 5dyne/cm or above from the ink separating layer. Therefore, the heated ink layer can generate an approximately 100% transfer to form an image on a body to be recorded.

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, such as plain paper, a recording method using a thermal transfer recording medium such as an ink donor film is widely adopted.

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, with the ink-coated base film facing the recording paper (plain paper), a thermal head selectively applies heat pulses from the back of the base film to remove the ink from that area. It is transferred onto recording paper by melting or sublimating it (Japanese Unexamined Patent Application Publication No. 1983-1999).
84735, etc.).

On the other hand, the energization transfer method is a method in which ink is applied, a needle electrode is brought into contact with the tape film, and the ink is selectively energized to heat the ink using 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 in which metals are dispersed in a resin and formed into a film (ribbon), or a highly resistive conductive polymer resin is used.

The ink layer contains a material with good conductivity (Imaging Electronics Engineers of Japan Journal, Vol. 11, No. 1, 1982).

In addition, although it is a similar method, instead of heating the ink by passing a current directly through it, the ink layer is applied 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
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, the thermal transfer recording medium 10 includes a base film 3
It has a structure in which a heating resistor layer 4, a conductive layer 5, and an ink layer 6 are laminated in this order on top.

This base film 3 is given a predetermined electrical conductivity. The needle electrode 1 and the return electrode 2 are brought into contact with the back surface of the thermal transfer recording medium 10. Here, the needle electrodes 1 are arranged in a large number of rows in a direction perpendicular to the plane of this paper, and electric pulses are selectively applied to some of them according to the image signal. Flow like arrow 12
The heat generating resistor layer 4 in the portion indicated by 2 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.
There is a time delay in recording due to the time required for heat conduction (time constant 1 m)
5ec), resulting in a slow printing speed.

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 the transfer control property is also poor. From this,
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. In addition to power loss due to electrical resistance within the base film, there is also loss due to current spread.
There are drawbacks such as poor power efficiency and low positional accuracy of recording dots. Furthermore, if a conductive material is incorporated into 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, since the base film 3 needs to have a sufficiently higher resistance than the heating resistor layer 4, the contact resistance with the needle electrode 1 etc. will inevitably become higher. 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 connection parts in the current path. However, there is a drawback that there is a large loss of electrical energy.

The present invention has been made with attention to the above points, and 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 heats an ink mainly composed of a thermoplastic polymer substance on a support and transfers the recording onto a recording medium. The support has an ink release layer on the side that supports the ink, and the critical surface tension of the ink support surface of the ink release layer is selected to be 33 dyne/cm or less.

The support also includes an ink release layer, a return electrode layer provided in this order on the lower surface thereof, a heating resistor layer, and an anisotropic conductive layer whose conductivity in the thickness direction is higher than the conductivity in the width direction. It is preferable that the

"Operation" The thermal transfer recording medium of the present invention is characterized by controlling the surface energy of the ink layer-bearing surface of the ink support to make the value efficient in terms of ink transfer and process. There is a particular thing. The surface energy of the ink-carrying surface is the most important factor in ink transfer, and the magnitude of this value determines whether transfer printing with hot melt ink is possible. Controlling this surface energy to a critical surface tension of 38 dyne/cm or less not only ensures complete ink transfer, but also eliminates the need for excessive heating in terms of energy. If the critical surface tension of the ink release layer is in the range of 38 to 5 Qdyne/cm, poor transfer occurs, and a large amount of ink heating is required to cause sufficient transfer, requiring a large amount of energy and resulting in poor efficiency. In addition, the critical surface tension of the ink release layer is 5
, Q d y n e /cm or more, ink transfer is difficult to occur, and even if the ink is heated, ink transfer of less than 30% by weight occurs.The surface energy of this ink support is controlled. This method utilizes the wetting properties of thermally melted ink, and is effective in any process that involves thermally melting ink and handling ink transfer.

Further, the anisotropic conductive layer is provided to allow current to flow with low loss in the thickness direction from the needle electrode in contact with the heat generating resistor layer. The heating resistor layer is a layer that generates heat using Joule heat caused by this current, and heats and transfers the ink. The return electrode layer serves as an electrode that diffuses and refluxes the current that has flowed into the heating resistor layer.

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. It is composed of a 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 200Ω.
Hereinafter, it is preferably selected to be 20Ω or less.

The heating resistor layer 24 is made of a material having heat resistance of 200'C or more, for example, ceramic such as TaN, and its volume resistivity is 10-2 Ω/unit cross-sectional area.
cm to 104Ω・cm, preferably 10Ω
・Select from cm to 103Ω・cm. In addition, from the viewpoint of the mechanical properties of the support, the thickness is from 3000 to 20 μm.
It is preferable to select a range of m.

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 x 10-' times lower than that of the heating resistor layer 24, preferably I x 10-'.
Select a material that is double the amount and has a heat resistance of 200°C 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 (TC) than that of the surface of a transfer material such as recording paper so that the ink can be easily transferred when heated. Preferably, it is an extremely thin film. Its thickness is selected to be 10 μm or less, preferably 1 μm or less.

When ink transfers to form a recorded image, the transfer force is due to the adsorption due to the mutual wetting of the ink, which is caused by the relationship in magnitude between the surface energy of the ink support surface to which the ink layer is attached and the surface energy of the transfer material surface. Power has a big influence. Due to the wetting of the semi-liquid heat-molten ink, the surfaces compete for the ink, and the ink adheres to the side with the stronger wetting adsorption force, that is, the one with the larger surface energy, thereby completing image formation. Based on the transfer mechanism, the surface energy (approximately equal to the critical surface tension) of the surface of the ink release layer of the ink support was selected to be 38 dyne/cm or less.

The surface energy of the transfer material, for example, plain paper, is 40 to 5 Qd.
yne/cm, OHP unit that is 40-45 dyn
e/cm. If an ink release layer having a critical surface tension difference of 5 dyne/cm or more from the critical surface tension of these general transfer materials is employed, the heated ink layer will undergo almost 100% transfer. Furthermore, by modulating the amount of heating of the ink layer, the semi-liquid ink is transferred in accordance with the amount of heating. That is, it becomes easy to control the area of the transferred dot by changing the input signal energy.

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 . The recording paper 33 is superimposed on this thermal transfer recording medium 30 and is conveyed by a pair of conveyance rollers 3.
4 and transported.

A recording head 35 in which needle electrodes 21 (Fig. 1) are arranged in a row.
is between the pair of conveyance rollers 34, and the back elastic roller 3
6, the thermal transfer recording medium 30 and the recording paper 33 are sandwiched together, and electric pulses for recording are 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 to the needle electrode 21, the linear body 23a, the heating resistor layer 23, and the anisotropic conductive layer 23.
and flows through the return electrode layer 25 as indicated 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 onto recording paper or the like. At this time, since the return electrode layer 25 and the ink peeling layer 28 are made sufficiently thin, the heat transfer rate is fast and energy loss is small.

By configuring the thermal transfer recording medium of the present invention as described above, the energy effectively utilized for recording with respect to the input energy is 15% or more, and recording can be performed with extremely high efficiency. Therefore, the energy supplied for recording is 1
It requires 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 Cu wires with a diameter of 25 μm are arranged in parallel at a density such that at least one wire exists in an area of 50 μm x 50 μm,
An anisotropic conductive layer was created by mold-curing with a thermosetting silicone resin. The surface was precision polished to a surface accuracy of 300 Å or more. Its thickness is 3 μm, the resistance value per unit area in the thickness direction (X direction in Figure 1) is 0.2Ω, and the resistance value in the plane direction (Y direction in Figure 1) is 1.
It was 0.012Ω or more.

■ Heat generating resistor layer 24 The anisotropic conductive layer obtained in step (2) was thoroughly washed and dried, and then placed in a vacuum system with a vacuum degree of 3 x 10-6 Torr.
After introducing argon gas to achieve X10-'Torr, a TaN target containing 20% by weight of Ai'203 was sputtered by high-frequency sputtering.
A heat generating layer having a resistance value of 150 Ω/10 −2 mm 2 and a thickness of 200 OA was formed.

■Return electrode layer 25 On the one obtained in (2), by electron beam vacuum evaporation method,
30OA of Cr at ultimate vacuum level 1.0XIO-6Torr
, 2000 AA films were deposited to obtain a return electrode layer.

(2) Ink release layer 28 A suspension Teflon dispersion was applied onto the return electrode layer and heat treated at 400°C to form an ink release layer with a thickness of 1 μm. The critical surface tension of this plane is 2Qdyne/
It was cm. This critical surface tension was measured by the Sisconfeld method.

0427 Layer 26 A yellow ink was prepared by mixing 9 weight percent of benzidine yellow pigment into a styrene-acrylic copolymer resin with a glass transition point of 60°C, and 13
An ink layer of μm pressure was formed.

The thermal transfer recording medium thus obtained was set in a device as shown in Figure 3, and needle electrodes with a diameter of 100 μm were inserted 8 pieces/m.
Recording was performed using line heads arranged at a density of m. Electric pulses for recording are 20V, 60V, 100V,
There were four types of 250V, all of which were rectangular pulses with a width of 200μSeC.

Plain paper for copying was used as the recording paper, and the line head was pressed against the back elastic roller with a rubber hardness of 35 with a pressure of 1.1 kg/cm2 to sandwich the thermal transfer recording medium and the recording paper. I did it. The return electrode layer 25 has a width of 250μ5eC1.
The electrodes were connected so that 30 square pulses were continuously applied.

In this way, thermal transfer recording was performed in accordance with the image signal, and transferred dots (recorded dots) were evaluated.

(Margin below) Table 1 Note that the ink transfer rate is the ratio of the amount of ink transferred to the transfer material to the amount of ink in the ink layer directly below the needle electrode.

(Comparative Example 1) In place of the ink release layer of the thermal transfer recording medium of the example, a film having a polyethylene tereclate resin deposited to a thickness of 1 μm was produced and evaluated in the same manner. The critical surface tension of the surface of this ink release layer was 43 dyne/cm.

Table 2 (Comparative Example 2) Among the thermal transfer recording media of the above examples, one without an ink release layer was manufactured and evaluated in the same way. At this time, the critical surface tension of the return electrode layer in contact with the ink layer is 68 d
It was yne/cm.

(The following is a blank space) Table 3 "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 as small as 200 μsec or less.
If a line head is used, high-speed printing of 1100 cp is also possible.

(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 a wide range of coloring materials (pigments and dyes) with unexpected color tones, and 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 human power signal is good, the amount of transferred ink can be adjusted by modulating the intensity of the human power signal. Therefore, it is possible to express the density of each dot in three or more levels, instead of expressing the gradation using a so-called dot matrix pattern method. Therefore, 6 to 8 pieces/m
While maintaining the high resolution of m, there are 8 to 16 levels of intermediate tones (
Halftone) expression is possible. 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) and 7 mm, it is economical to record with an energy of 100 to 700 ergs per dot.

(5) High reliability.

By managing the resistance value of the heating resistor layer, the heating pattern can be controlled.
Furthermore, if a heat-resistant material such as ceramic is used for this heating resistor layer, it can be easily manufactured while controlling its thickness to several tens of angstroms. Moreover, the process (recording operation) operates stably in the range of humidity 10 to 90% (Rh) and temperature 5 to 30°C, and high reliability can be obtained. Therefore, there is no need for humidity control when handling powder as in a laser printer or electrostatic recording method, or temperature control for stabilizing ink viscosity as in an inkjet method, and maintenance management is easy.

(6) Since the ink layer is formed on the ink release layer having a critical surface tension of 33 dyne/cm or less, the efficiency of ink transfer is high, the image quality is improved, and the reliability of recording is increased. Additionally, this provides stable characteristics against changes in environmental temperature and humidity, making it possible to perform good recording even in slightly cold conditions, for example, by adjusting the human energy. This will further improve overall reliability.

[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 the anisotropic conductive layer thereof, and FIG. 3 is a schematic configuration diagram of a recording device using the thermal transfer recording medium of the present invention. FIG. 4 is a longitudinal sectional view of a conventional thermal transfer recording medium. 20... Support body, 23... Anisotropic conductive layer, 23a... Linear body, 24... Heat generating resistor layer, 25... ... Return electrode layer, 26 ... Ink layer, 28 ... Ink release layer. Applicant: Fuji Xerox Co., Ltd. Agent

Claims (1)

[Scope of Claims] 1. An ink mainly composed of a thermoplastic polymer substance on a support is heated and transferred onto a recording medium, wherein the support has a side that carries the ink. 1. A thermal transfer recording medium, comprising: an ink release layer; and a critical surface tension of the ink carrying surface of the ink release layer is selected to be 38 dyne/cm or less. 2. The support includes an ink release layer, a return electrode layer provided on the lower surface of the ink release layer, a heating resistor layer, and an anisotropic conductive layer having a higher conductivity in the thickness direction than in the width direction. A thermal transfer recording medium according to claim 1, characterized in that the thermal transfer recording medium comprises: