JPH0461788B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to the improvement of a current transfer recording sheet, and its purpose is to (1) reduce the resistance value by using a specific solid component in the current flow resistance layer;
The objective is to (2) improve heat resistance and (3) improve adhesion to the support layer, thereby reducing the voltage applied to the current-carrying head, reducing dirt on the current-carrying head, and improving image quality. In recent years, thermal transfer recording has attracted attention in many fields such as facsimile machines, computer terminals, and recorders because it has features such as non-impact, noiseless, maintenance-free, low cost, can be made smaller and lighter, and can be colored. . Among these methods, the method of electrical thermal transfer using a current-carrying head is particularly suitable for full-color recording with intermediate gradations, and is the method that is attracting the most attention as a promising future hard copy method. For details on electrical thermal transfer recording, see, for example, "Nikkei Electronics" 64-68.
See Page, June 25, 1979. FIG. 1 shows a principle diagram in which current is applied to a current-carrying transfer recording sheet 1 by a current-carrying head having a current-carrying recording electrode 5 and a return electrode 6. The current-carrying head is connected to a current-carrying resistance layer 2 of the recording sheet. The ink layer 4 is brought into contact with pressure and energized to generate heat and heat up the resistance layer, and the heat is transferred to the support layer 3, causing the ink layer 4 to rise in temperature and melt and flow, thereby thermal transfer recording is performed on the recording paper. (The recording paper is not shown). Here, the most important performance required for the resistance layer of the current thermal transfer method is (1) the resistance value of 10 ² to 5 × 10 ⁵ Ω/
(2) At least the resistance layer should be lowered to □.
(3) We want to have short-term heat resistance of 285℃ or higher.
The adhesion of the resistance layer to the support layer is sufficient against the shearing frictional force caused by the pressing contact of the current-carrying head;
etc. However, the current situation is that all of the current-carrying resistance layers that have been proposed so far are insufficient in meeting these required performances. These problems and the inventors' ideas for solving them will be described in order. The first thing to do is to reduce the resistance value. In this case, in order for the resistance layer to generate heat when energized, the resistance value of the resistance layer must be between that of an insulator and a good conductor, and the resistance value is determined by the amount of electricity applied, the thermal conductivity of the recording sheet , is set based on the balance of the melting energy of the ink layer, etc. To generate heat in the resistance layer,
Conventionally, there has been a method of forming a resistive layer by dispersing metal powders such as aluminum, copper, iron, tin, zinc, nickel, molybdenum, silver, etc. in a resin binder as conductive dispersed particles (Japanese Patent Laid-Open No. 56-86790~ 1977-
86793), method of dispersing copper iodide in a resin binder (JP-A-51-106445), method of dispersing zinc oxide and titanium dioxide in a resin binder (JP-A-53-74047), supporting conductive polymer Method for applying to body layer (Japanese Patent Application Laid-Open No. 51-106445), graphite,
A method of dispersing acetylene black in a resin binder (Japanese Patent Application Laid-Open No. 56-27382) has been proposed. The present inventors have also thoroughly considered the various proposals mentioned above. Among these methods, it has good affinity with the resin binder and can be uniformly dispersed in the binder in the form of fine particles, and also has good affinity with the solvent that dissolves the binder resin and can be well dispersed in the solvent. It has been found that relatively inexpensive conductive particles are carbon-based particles such as graphite and acetylene black. Examples of carbon-based particles include the above-mentioned graphite and carbon black. Carbon black can be manufactured using the furnace method, channel method, formal method, etc., and there are many types of particle characteristics. . Among these, graphite and acetylene black have good conductivity among carbon particles, and have been kneaded into polymers to be used in surface heating elements, antistatic materials, surface switches, packaging materials, etc. It is used. The lower the resistance value of the current-carrying resistance layer developed by the present inventors, the smaller the voltage applied to the current-carrying head. Therefore, the capacity of the power supply and drive system for the head can be reduced, making it more reliable and less expensive. Can be done. The surface resistance value is 10 ² to 5×10 ⁵ Ω/□, preferably
I want to set it to 10 ³ to 10 ⁴ Ω/□. However, it has been found that when a resistive layer is formed using a conventional conductive filler such as graphite or acetylene black, it is difficult to reduce the surface resistance value to 5×10 ⁵ Ω/□ or less. If the filling amount of graphite or acetylene black is increased to 35 to 40% by weight or more, it is possible to achieve a resistance of about 3 x 10 ⁵ to 5 x 10 ⁵ Ω/□, but it is difficult to apply the resistance layer to the support layer. In addition, the mechanical strength and the adhesion of the resistance layer to the support layer deteriorate when the current-carrying head is brought into pressure contact with the resistance layer, making it impractical for practical use. The inventors of the present invention have repeatedly searched and studied all types of carbon-based particles in order to lower the resistance value.
It has been found that carbon black with a DBP oil absorption of 300 ml/100 g or more is effective. Such a carbon black has recently been commercially available as a special oil furnace black called "Ketschen Black" (trade name) developed by AKZ0 Chemie of the Netherlands. Ketchen Black has been kneaded in bulk with general-purpose resins such as polyethylene and polypropylene to form a compound and used for surface heating elements, wire-coated cables, antistatic agents, etc. The present inventors also made a compound by kneading Kettien Black in bulk with a binder resin such as polyvinyl chloride/vinyl acetate copolymer, polybutyral, polyurethane, phenoxy resin, nitrocellulose, or polyester in the same manner as before. Thereafter, a resistive layer was formed by dissolving it in a solvent and applying the solution onto the support layer. However, the surface resistance value is 5
It could not be lowered below ×10 ⁵ Ω/□. Also,
A resistive layer was formed by melting a polyvinyl butyral compound at around 120°C and applying it onto a support layer using a hot melt method. In this case as well, the surface resistance value could not be lowered below 5×10 ⁵ Ω/□. The inventors of the present invention conducted further studies and determined that KETSUCHEN BLACK was used in a ball mill in a solution system of a solvent that dissolves other solid components (the main component is a resin component that serves as a binder) constituting the current-carrying resistance layer. After dispersing the solution, the solution is applied to the support layer and the solvent is dried to form a resistive layer, which significantly reduces the surface resistance value to 5×10 ⁵ Ω/□ or less, 10 ³
We obtained the remarkable result that it was possible to reach ~10 ⁴ Ω/□. Next is the issue of heat resistance. Due to heat generated by electricity,
The resistance layer and the support layer were measured to reach a temperature of 150 to 350°C, although it was for a short time of 20 μsec to 20 msec.
Polyimide film and capacitor paper are recommended materials for the support layer in terms of heat resistance.
It is difficult to manufacture a thin film of 2 to 10 .mu.m with these methods, and from the viewpoint of thermal conductivity, a thin film of 10 .mu.m or less, which is necessary for transferring delicate intermediate gradations, cannot be provided. Furthermore, polyimide film is very expensive and is not suitable for disposable use. From the balance of film thickness, heat resistance, mechanical strength, and price,
As the material for the support layer, a biaxially stretched polyethylene terephthalate (PET) film must be selected. However, when PET film is used as the support layer,
If the resistance layer has low heat resistance, the PET film will melt along the path of the current-carrying head needle, causing holes to form, which is a major problem. This significantly reduces image quality and sometimes causes troubles due to the head needle sticking. The highest temperature of the resistive layer and support layer is the upper surface of the resistive layer that is in contact with the current carrying head. Therefore, it has been found that improving the heat resistance of the resistance layer is an essential condition, and that if the heat resistance of the resistance layer is improved, the PET film of the support layer will not melt. That is,
The heat-resistant resistance layer serves as a barrier to the support layer PET film against heat. Regarding the heat-resistant binder material, the present inventors
Many resins were considered. It is not sufficient for a heat-resistant binder to have only excellent heat resistance. Dispersibility of carbon particles, adhesion to PET film, rheological properties of coating, etc. must also be considered. It has been difficult to find a heat-resistant binder that satisfies these conditions. for example,
Polyvinyl chloride/vinyl acetate copolymer (PVCl/
VAC) and polyvinyl butyral (PVB) have very good dispersibility of carbon particles, but they have poor heat resistance and cause holes in PET films. Nitrified cotton also has fairly good dispersibility, but its heat resistance is somewhat lacking, and there are holes in areas with high density images. Modified polyester has very good adhesion to PET film, but has only moderate heat resistance and very poor carbon particle dispersibility. As a result of many studies, the present inventors have found that a phenoxy resin crosslinked with at least one crosslinking agent such as polyisocyanate, melamine-formaldehyde, phenol-formaldehyde, urea-formaldehyde, etc., is suitable for the purpose of the present invention. We have discovered that this method has a remarkable effect on improving the heat resistance of the current-carrying resistance layer of the current-carrying thermal transfer method. As a result of temperature measurement, the phenoxy resin crosslinked material passed the short-term heat resistance of 300℃ or more, and it was biaxially stretched with a melting point of 265 to 270℃.
We discovered that there are no holes in PET film either. Based on this result, the present inventors first developed a recording sheet for electrical thermal transfer that contains a phenoxy resin and its crosslinking agent in the solid components of the electrical resistance layer in order to improve heat resistance. We made a proposal and applied for a patent. However, the crosslinked structure of phenoxy resin also has some drawbacks. The dispersibility of carbon particles is
PVCl/VAC and PVB are very good, followed by nitrified cotton, and phenoxy resin ranks next. The dispersibility of carbon particles affects the image quality, especially the image quality in the intermediate gradation region, and if the dispersibility is poor, the intermediate gradation region in particular becomes patchy. The heat resistance (temperature at which holes form in PET film due to melting) of a crosslinked structure made of nitrified cotton crosslinked with polyisocyanate is 285 to 300°C, which is slightly lower than that of a phenoxy resin crosslinked structure, but PVCl/
Much better than VAC or PBT. With nitrified cotton, there may be holes in the PET film at the power application point at full density, but there will be no holes in the PET film at the power application point in the low density to intermediate gradation range, and the current-carrying head needle will not damage the PET film. Trouble due to status,
Dirt on the current-carrying head is not a big problem. The image quality is even better than that of phenoxy resin. The present inventors propose an electrical transfer recording sheet using as a resin binder a crosslinked structure of nitrified cotton, which has been found to be effective in improving heat resistance and dispersibility. The third point is the problem of adhesion to PET film. Although nitrified cotton has excellent heat resistance and carbon particle dispersibility is quite good, its adhesion to PET film is only moderate. According to the peeling test method using cross-cut adhesive tape at 1 mm intervals, 60
% will be released. Therefore, we further investigated ways to improve the adhesion of nitrified cotton as a binder.
I tried applying corona discharge to the PET film to activate its surface, but the effect on adhesion did not improve at all. A thin layer of modified polyester (0.3-1μ
After undercoating m) on PET film,
When nitrified cotton is applied, the adhesion improves considerably, and the cross-cut method shows that peeling is about 10 to 15%. However, the undercoating method requires an additional production step due to the undercoating, which increases the price of the recording sheet. Therefore, we investigated a resin material that can be blended with nitrified cotton to improve adhesion. In this case, the properties required of the material for improving adhesion are (1) good compatibility with nitrified cotton, (2) good dispersibility of carbon particles,
(3) Heat resistance is good to some extent. Epoxy resin, phenolic resin, modified polyester,
After examining PVB, PVCl/VAC, polyurethane, etc., we found that polyurethane best satisfies the above-mentioned required properties if the amount of blending is specified. Polyurethane not only improves adhesion, but also
It also has the effect of softening the coating film based on cross-linked nitrified cotton, which is hard and lacks flexibility. As mentioned above, the most important demands for improvement of the current-carrying resistance layer are (1) reduction in resistance value, (2) improvement in heat resistance, and (3) improvement in adhesion. After repeated consideration to meet these demands,
Although the material of the present invention has been found, it does not mean that the aforementioned materials can be contained in unlimited proportions.
The content ratio of these materials, resistance value, heat resistance,
Each adhesion function functions as a variable. Therefore, according to the specifications of the hardcopy machine, after all,
Depending on the designed resistance value, heat resistance, and adhesion of the current-carrying resistance layer, the content ratio of the above-mentioned materials changes slightly within a certain range. As detailed above, we have made extensive studies to improve the various drawbacks of the current-carrying resistance layer, for which the current proposals are inadequate, and as a result we have come up with the invention of a new current-carrying transfer recording sheet. That is, the present invention provides a recording sheet for current-carrying thermal transfer consisting of a current-carrying resistance layer, a support layer, and an ink layer, which generates heat in the resistance layer by energization and thermally transfers the ink layer to a recording paper to obtain a record. The resistance layer contains at least the following solid components (1) to (4):
Carbon black of 100g or more C _K = 5 ~
35% by weight (2) Nitrified cotton with a nitrogen content of 10.7 to 12.2% and an average degree of polymerization of 30 to 300, C _N = 20 to 60% by weight (3) Polyurethane, Cu = 10 to 50% by weight (4) The above nitrified cotton and C _C = 5 to 25% by weight of polyisocyanate as a crosslinking agent for polyurethane;
and the sum of the solid components of (1) to (4) above satisfies (5) C _K + C _N + Cu + C _C = 80 to 100% by weight, and the support layer is (6) polyethylene terephthalate. thickness consisting of 2
It consists of a biaxially stretched film of ~10 μm (7) The surface resistance value of the current carrying resistance layer is 10 ² ~ 5×10 ⁵
This is an electrical transfer recording sheet characterized by satisfying all of the above (1) to (7) in the range of Ω/□. In the present invention, the measurement of DBP oil absorption is performed using JIS
This is based on K6221's oil absorption measurement method A, in which dibutyl phthalate (DBP) is absorbed into carbon black using an absorbometer. There is a strong correlation between the DBP oil absorption of carbon-based particles and the surface resistance value of a resistance layer coated by a solution method. If the DBP oil absorption is less than 300ml/100g,
It is difficult to reduce the surface resistance value to 5×10 ⁵ Ω/□ or less. It has been found that if carbon particles have a DBP oil absorption of 300 ml/100 g or more, the surface resistance value can be increased to 10 ² to 5×10 ⁵ Ω/□, although the exact reason is not well understood. Acetylene black with good conductivity has a DBP oil absorption of 210 to 280 ml/100 g. DBP oil absorption
Examples of carbon particles of 300 ml/100 g or more include Ketschen Black (trade name). The DBP oil absorption of Ketschen Black is 300-450ml/100g. Carbon particles with a DBP oil absorption of more than 450ml/100g have not yet been found in the world. The DBP oil absorption of normal carbon black for rubber and carbon black for color is 50 to 150ml/100g, and the surface resistance value when used in a resistance layer is 10 ⁶ to 10 ⁷
It is on the order of Ω/□ and cannot be used for the purpose of the present invention. The carbon-based particles used to achieve the object of the present invention are preferably Ketchen Black. It is essential that the dispersion of Ketchen Black in the binder resin be carried out in a solution. Ketsutien black has a carboxyl group content of approximately 0.5 meq/g, a total acidity excluding carboxyl groups of approximately 0.3 meq/g, and although it has polar groups, it does not float in the toluene phase in the water/toluene two phases. However, it is essentially lipophilic. Therefore, it is possible to uniformly disperse Ketchen Black in a lipophilic organic solvent solution containing a binder resin by dispersing it in a ball mill for approximately 24 to 48 hours and in an attritor for 6 to 12 hours. I can do it. In the electrical thermal transfer method, the uniformity of the dispersion of the resistance heating particles has a large effect on the image quality of the print. In the case of a bulk compound in which Ketchen Black is kneaded and dispersed in a binder resin, uniform dispersion is impossible, and the surface resistance value is 10 ⁶ to ^{10 7} Ω/□. The amount of carbon black in the solid component of the resistance layer is 5 to 35% by weight, preferably 10 to 25% by weight.
It is. In this way, the DBP oil absorption amount is 300ml/100
A feature of the present invention is that when using carbon black with a weight of 1.5 g or more, the surface resistance value can be lowered even though the carbon black content is extremely small. However, the carbon black content is 5
If it is less than % by weight, the surface resistance value cannot be lowered to 5×10 ⁵ Ω/□ or less. On the other hand, when the carbon black content exceeds 35% by weight, the surface resistance value decreases to approximately 10 ²
Although it can be made into Ω/□, the resistance layer becomes brittle in terms of mechanical strength and is easily peeled off from the support layer. Furthermore, coating cannot be performed smoothly and streaks occur in the coated product. The carbon black content is set within the range of 5 to 35% by weight and is increased or decreased depending on the design resistance value. The resin used in the present invention to improve the heat resistance of the resistance layer has a nitrogen content of 10.7 to 12.2% and an average degree of polymerization.
30~300 industrial nitrified cotton. The degree of polymerization is n=30
-300, preferably n=50-150. When the degree of polymerization is n<30, the dispersibility of the carbon particles is good, but the heat resistance and the mechanical strength of the coating film are considerably poor and cannot be put to practical use. On the other hand, when n > 300, heat resistance and mechanical strength are excellent, but the dispersibility is poor, resulting in unevenness in the thermally transferred image, unsatisfactory image quality in intermediate gradation areas, and poor coating film quality. My curls get worse. Nitrified cotton has an average of 1.9 to 2.3 hydroxyl groups per repeating unit. The reason why the carbon particle dispersibility is quite good may be due to some kind of chemical bond or van der Waals force bond with the carboxy group on the surface of the carbon particle. In the present invention, the hydroxyl groups of nitrified cotton are used to carry out a crosslinking reaction with polyisocyanate. If nitrified cotton is used alone without a crosslinked structure by a crosslinking agent, the resistance layer will not have a heat resistance of 285°C or higher. Examples of the polyisocyanate include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, diphenylmethane-4,4'-diisocyanate, and a reaction product of 3 moles of 2,4-tolylene diisocyanate and 1 mole of trimethylolpropane. ,3,
3'-vitrylene 4,4' diisocyanate, 3,
Examples include 3' dimethyl diphenylmethane 4,4' diisocyanate and 2,4 tolylene diisocyanate dimer (uretidine dione), but a reaction product of 4 tolylene diisocyanate and trimethylolpropane is preferred. It is desirable to sufficiently disperse carbon black in nitrified cotton and polyurethane in an organic solvent, and then add a crosslinking agent and stir and mix immediately before coating. In order to sufficiently carry out the crosslinking reaction and improve heat resistance,
After coating and solvent evaporation drying, at 40-60℃ for 24-48 hours,
It is desirable to carry out a curing reaction. As the polyurethane used in the present invention to improve adhesion to the PET film of the resistance layer, commercially available polyurethane adhesives can be used. For example, polyesters with more than two functional groups, polyethers reacted with TDI, MDI, etc.,
There are prepolymers produced by the reaction of diisocyanates and polyfunctional active hydrogen compounds. The crosslinking agent reacts not only with the hydroxyl groups of the nitrified cotton but also with the active hydrogen in the urethane bonds of the polyurethane to form a crosslinked structure and improve heat resistance. but,
Heat resistance is insufficient if there is no nitrified cotton and the crosslinked structure is created using only polyurethane as a crosslinking agent. The content ratio of nitrified cotton/polyurethane is 3/7~
It is 7/3, preferably 4/6 to 6/4. The content of nitrified cotton in the solid components of the resistance layer is C _N = 20 ~
It is 60% by weight. If C _N < 20%, heat resistance 285
℃ or more is not possible. On the other hand, if C _N >60%, the adhesion will be insufficient and the coating film will curl severely. The content of the crosslinking agent is C _C =5 to 25% by weight.
It is. When C _C <5, the heat resistance is poor; on the other hand, when C _C >
In the case of 25, the resistance value will become large, and
Adhesion becomes insufficient. The content of polyurethane is Cu=10-50% by weight. When Cu<10%, there is almost no difference in adhesion compared to when no polyurethane is contained. On the other hand, Cu>50%
In the case of , the adhesion is extremely good, but the heat resistance is reduced. Among the solid components of the resistance layer, the total sum of carbon black (C _K ), nitrified cotton (C _N ), crosslinking agent (C _C ), and polyurethane (Cu) is Σ=C _K +C _N +Cu+C _C =80~
It is 100% by weight. That is, materials other than the above four types may be contained within a range of less than 20%. for example,
These include softeners, anti-wear agents, antistatic agents, lubricants, smoothing agents, binder resins, and conductive particles. A particularly preferred example is the addition of polyvinyl chloride/vinyl acetate copolymer, which suppresses the curling tendency of nitrified cotton and further improves the dispersibility of carbon particles. You may add less than that. When Σ<80%, any one of the performances of dispersibility, resistance value, heat resistance, and adhesion will be greatly reduced, and the current-carrying recording sheet that is the object of the present invention cannot be obtained. The thickness of the PET film of the support layer is 2 to 10 μm.
and preferably 4 to 7 μm. The thinner the film, the better the heat transfer efficiency, the less applied power, and the sharper the image quality. It is difficult. On the other hand, if it exceeds 10 .mu.m, the heat transfer efficiency will be poor, the applied power will be large, the dot diameter of the print will become large due to lateral heat diffusion, and the resolution of the image quality will deteriorate. It is preferable that a crosslinking agent is added to a dispersion liquid in which nitrified cotton and polyurethane are dissolved individually or simultaneously in an organic solvent and carbon black particles are dispersed using a ball mill, an attritor, etc., and the mixture is stirred and mixed immediately before coating. . As the coating head of the coating machine, a reverse roll, gravure roll, gravure offset roll, doctor blade, wire bar, etc. can be used. The solid component concentration of the coating liquid is 10~
40% by weight, preferably 20-30% by weight. After coating, the solvent is evaporated and dried in a drying oven. The crosslinking reaction between nitrified cotton and polyurethane using a crosslinking agent is carried out to some extent even in a drying oven, but in order to achieve a sufficient reaction, it is desirable to perform the treatment in a separate step under the above-mentioned conditions. The ink layer (4 in FIG. 1) is applied to the support layer 3 on the side opposite to the current-carrying resistance layer 2 by a hot melt method or a solution method. The ink layer contains approximately 60% by weight of wax such as paraffin wax, modified wax, carnauba wax, etc., and 20% by weight of color material pigment or dye.
It is desirable to have a resin content of 20% by weight. The ink composition containing pigments or dyes such as yellow, cyan, magenta, and black may be applied in one color, as shown in 4 in FIG. 1, or in a second color.
As shown in FIGS. 4 (41 to 44), the coating may be applied in a uniform manner in the longitudinal direction. The surface resistance value of the current carrying resistance layer of the present invention described in detail above is in the range of 10 ² to 5×10 ⁵ Ω/□. Preferably it is 10 ³ to 10 ⁴ Ω/□. In this way, we were able to reach a small resistance value because the PBP oil absorption amount was 300ml/
This was achieved by using 100 g or more of carbon black, dispersing it in a solution in a binder resin, and applying it by a solution method. The current-carrying resistance layer of the present invention has short-term heat resistance of 285 to 310°C, and when the power applied to obtain the highest concentration (optical density 0D≒1.5) is applied, the PET film layer melts and holes form. However, at low to mid-tone densities, the problem of holes was completely resolved. This mainly involves containing a specific amount of specific nitrified cotton,
This is due to the effect of forming a crosslinked structure with the crosslinking agent. The adhesion between the current-carrying resistance layer and the support layer of the present invention is almost perfect. Peeling test results for adhesive tapes using crosscuts at 1 mm intervals show that peeling is within 15%. This is due to the effect of containing a specific amount of polyurethane. The electrical transfer recording sheet of the present invention has the following advantages. (1) By setting the surface resistance to 10 ³ to 10 ⁴ Ω/□, the applied voltage can be lowered to 15 to 50 V, making it possible to reduce the cost of the IC that drives the current-carrying head. In addition, the power source can be made inexpensive. (2) The applied voltage can be lowered, reducing discharge,
The life of the current-carrying head is dramatically improved. (3) Since the discharge of the current-carrying head is reduced, the amount of shavings of the resistance layer adhering to the head is dramatically reduced, which improves maintenance. (4) Since the carbon black is uniformly dispersed,
The image quality has improved, and subtle intermediate tones can now be printed clearly. (5) Improved heat resistance almost eliminates holes in the PET film, eliminates troubles caused by the stay of the current-carrying head, eliminates troubles caused by holes, and eliminates contamination of image quality caused by holes. (6) Improved adhesion eliminates spot peeling of the resistive layer and adhesion of peeling debris of the resistive layer to the current-carrying head during thermal transfer. The present invention will be explained below with reference to Examples. Of course, the present invention is not limited to this. The methods for measuring DBP oil absorption, surface resistance, heat resistance, and adhesion defined in the present invention are as follows. (1) DBP Oil Absorption JIS K6221 Oil Absorption Measurement Method A (2) Surface Resistance Value Place the current-carrying resistance layer on top on a smooth flat table, and place a pair of gold-plated brass electrodes (5 mm width, 35 mm
length, weight 350g) in parallel on the current carrying resistance layer,
Place the electrodes with a spacing of 35 mm, and measure the resistance value with an electrometer. The measurement room has an environment of 25°C and 65% relative humidity. (3) Heat resistance Using a standard current-carrying resistance layer, create a calibration curve in advance of the relationship between the amount of power obtained from the applied voltage and current of the current-carrying head and the temperature measured from an infrared thermometer, and Head power is gradually applied to the resistance layer sample, and a transmission optical microscope is used to evaluate the temperature at which a hole is formed in the PET film support layer due to melting, and this temperature is used as a measure of heat resistance. shall be. Heat resistance is sufficient when there are no holes in the PET film at full density (optical density 0D = 1.4 to 1.5) of the thermal transfer image of color material black. (4) Adhesion Using a cross-cut tester (manufactured by Toyo Seiki), a PET film coated with a resistance layer was placed on a steel plate, and the PET film was tested under a load that did not cut the PET film.
Cut the resistance layer crosswise into 10 pieces vertically and 10 pieces horizontally at 1 mm intervals, peel it off with adhesive tape, and use the number of pieces that remain without peeling as a measure of adhesion (%). Examples 1 to 2 and Comparative Examples 1 to 5 As shown in Table 1, various carbon blacks were dispersed in the following binder resin, applied to a PET film as a support layer, and the solvent was evaporated and dried.
After performing the crosslinking reaction, the surface resistance value was measured. (1) Dispersion conditions Carbon black; 15 parts (weight) Nitrified cotton (Asahi Kasei, Cellnova BTH1/2, nitrogen content
11.5-12.2%, average degree of polymerization 88); 30 parts polyvinyl chloride/vinyl acetate copolymer (UCC, VYHH)
; 13 parts polyurethane (Japan Polyurethane, N-
2304); 30 parts polyisocyanate (Japan Polyurethane, Coronate L) 12 parts MEK/toluene = 1/1; 400 parts Dispersion is performed by removing the polyisocyanate and dispersing in a ball mill for 24 hours, then adding the polyisocyanate and stirring immediately before coating. Mixed. (2) Coating Support: Biaxially stretched PET film (8 μm) Coating machine: 3-roll reverse roll coater Coating speed: 20 m/min, coating thickness approximately 4 μm (dry thickness) Drying: Hot air at 150°C, Furnace length: 4m (3) Curing reaction: 80℃ for 20 minutes, then 45℃ for 24 hours (4) Results

[Table] As shown in Table 1, there is a strong correlation between surface resistance value and DBP oil absorption, and the resistance value targeted by the present invention
To set 10 ² to 5×10 ⁵ Ω/□, the DBP oil absorption should be
300ml/100g is required. DBP oil absorption is 300
ml/100g or less carbon particles (Comparative Examples 1~
In the case of 5), when the filling amount of carbon particles is about 15wt% as in this experiment, the surface resistance value is set to 5×10 ⁵ Ω/
□It cannot be done below. Examples 3 to 5 and Comparative Examples 6 to 7 Various brands (average degree of polymerization) of nitrified cotton (nitrogen content 11.5 to 12.2%) were used, and KETSUEN BLACK (DBP oil absorption 345 ml/100 g), polyisocyanate, polyurethane, Solvent (MEK/toluene = 1/1,
A resistive layer was formed using the same dispersion conditions (solid component composition), solution coating conditions, and crosslinking reaction conditions as in Examples 1 and 2 above. Their surface resistance, heat resistance (temperature at which holes are made in PET film and optical microscope observation), and adhesion were measured.
The results are shown in Table 2.

[Table] In Comparative Example 6, there were holes in the PET film support layer even in the medium density printing area. Comparative example 7 has a solid content concentration of 25
Since it could not be dispersed at a concentration of 10% by weight, it was coated after being dispersed at a concentration of 10%. However, the resistance values vary widely and cannot be used for image processing. Adhesion also tends to be slightly inferior. Examples 3 to 5 were satisfactory in terms of resistance, heat resistance, and adhesion. In addition, Example 5
was also dispersed at a concentration of 10%. Examples 6 to 16 and Comparative Examples 8 to 15 Ketchen Black (DBP oil absorption 345ml/100
g), nitrified cotton, polyisocyanate, and polyurethane at various contents shown in Table 3 (the brand of resin used is the same as in Examples 1 and 2), and a solvent (MEK/
Toluene = 1/1, solid content concentration 25% by weight), and other dispersion conditions, solution coating conditions, and crosslinking reaction conditions were the same as in Examples 1 and 2 to form a resistive layer. Their surface resistance, heat resistance (temperature at which holes are made in PET film and optical microscope observation), and adhesion were measured. The results are shown in Table 3. In Comparative Example 8, which has a small content of carbon black, the resistance value does not fall below 5×10 ⁵ Ω/□. On the other hand,
When the amount of carbon black is as high as 43%, coating spots become large, resistance values vary, and holes appear in the PET film even in the low to medium density range (Comparative Example 9). If the content of nitrified cotton is as low as 15%, holes will form even in the low concentration range, resulting in considerably poor heat resistance (Comparative Example 10). On the other hand,
When the amount of nitrified cotton increases to about 65%, coating spots become large and adhesion deteriorates significantly (Comparative Example 11). If the crosslinking agent (polyisocyanate) is around 3%, holes will form even in the low concentration range and there will be no heat resistance.

[Table] (Comparative Example 12). On the other hand, when the amount of crosslinking agent increases by nearly 30%, coating spots become larger and the resistance value decreases to 5×10 ⁵ Ω/
□ or above, and the heat resistance temperature also tends to decrease (Comparative Example 13). 5% polyurethane
If the amount is extremely small, the adhesion will decrease significantly (Comparative Example 14). On the other hand, when the amount of polyurethane increases to around 60%, the nitrified cotton content becomes relatively low.
Heat resistance decreases and holes form even at low to medium concentrations (Comparative Example 15). In Examples 6 to 16, in terms of surface resistance, heat resistance, and adhesion, there were some holes in the PET film at the full concentration of 0D = 1.4 to 1.5, but they provided satisfactory current carrying resistance layers that could withstand practical use. He did it for me. Example 17 The coating layer obtained in Example 13 was used as a current-carrying resistance layer, and yellow, magenta, cyan, and black ink layers were sheeted on the opposite side of the resistance layer with a support layer in between, as shown in Figure 2. Hot melt coating was applied in the longitudinal direction of the plate. (1) Ink layer composition Pigment: 20 parts by weight Parafine wax: 20 parts Oxide wax: 40 parts Polyethylene/vinyl acetate copolymer: 20 parts Stearic acid: 3 parts Dispersed using a roll mill. (2) Ink layer coating Coating materials: 4 hot melt gravure rolls (120°C) and smoothing bar (120°C) Coating speed: 20 m/min Example 18 The ink layer of the present invention obtained in Example 17 above Using a current transfer recording sheet, as shown schematically in Fig. 1,
Full-color printing was performed on A4 size plain paper using a current-carrying head having a recording electrode 5 and a return electrode 6. (1) Current-carrying head Dot pitch: 6 dots/mm Line pitch: 6 dots/mm Head needle diameter: 60 μm (2) Drive Applied voltage: 25 V Pulse width modulation: 50 μsec to 1.6 milliseconds 32 gradations (3) Full color printing result Color silver A salt photograph was used as the original, and after color separation using a color scanner, it was converted into 32 gradation signals, and after gamma correction, it was printed in full color. Printed matter using the current transfer recording sheet of the present invention produced a beautiful color image with gradation that was extremely close to the original image. Furthermore, since the resistance value of the resistive layer is low, on the order of 10 ³ Ω/□, we succeeded in printing with an extremely low driving voltage of 25V.

[Brief explanation of the drawing]

FIG. 1 shows the structure of a current-transfer recording sheet and a diagram of the principle of energizing it by a current-carrying head, and FIG. 2 shows an embodiment of the structure of the current-transfer recording sheet of the present invention. DESCRIPTION OF SYMBOLS 1... Current transfer recording sheet, 2... Current carrying resistance layer, 3... Support layer, 4 and 41 to 44... Ink layer, 5... Recording electrode, 6... Return path electrode.

Claims (1)

[Scope of Claims] 1. A recording sheet for current-carrying thermal transfer consisting of a current-carrying resistance layer, a support layer, and an ink layer, which generates heat in the resistance layer by energization to thermally transfer the ink layer to a recording paper to obtain a recording, comprising: The current-carrying resistance layer contains at least the following solid components (1) to (4):
Carbon black of 100g or more C _K = 5~
35% by weight, (2) Nitrified cotton with nitrogen content of 10.7-12.2% and average degree of polymerization of 30-300, C _N = 20-60% by weight, (3) Polyurethane, Cu = 10-50% by weight, (4) Above Polyisocyanate as a crosslinking agent for nitrified cotton and polyurethane, C _C = 5 to 25% by weight,
and the sum of the solid components of (1) to (4) above satisfies (5) C _K + C _N + Cu + C _C = 80 to 100% by weight,
The support is made of (6) polyethylene terephthalate with a thickness of 2
It consists of a biaxially stretched film of ~10 μm (7) The surface resistance value of the current carrying resistance layer is 10 ² ~ 5×10 ⁵
An electrical transfer recording sheet that is in the range of Ω/□ and satisfies all of the above (1) to (7).