EP0124616B1

EP0124616B1 - Heat-sublimable ink ribbon

Info

Publication number: EP0124616B1
Application number: EP19830903408
Authority: EP
Inventors: Yoshio Sony Chemicals Corporation Fujiwara; Junetsu Sony Corporation Research Center Seto; Shigemichi Honda; Naotake Sony Chemicals Corporation Kobayashi; Tetsuya Sony Chemicals Corporation Abe; Satoru Sony Chemicals Corporation Shinohara
Original assignee: Sony Corp
Current assignee: Sony Corp
Priority date: 1982-10-29
Filing date: 1983-10-25
Publication date: 1988-05-11
Also published as: DE3376541D1; JPH0471718B2; WO1984001746A1; EP0124616A1; EP0124616A4; JPS5979788A

Abstract

A heat-sublimable ink ribbon comprising a heat-resistant base sheet and a heat-sublimable ink formed on the base sheet surface. The ink comprises a sublimable ink, a binder, and 30 to 200 parts by weight, per 100 parts by weight of the sum of the dye and the binder, of solvent-insoluble particles with high thermal conductivity uniformly dispersed in the binder and dye. The use of this ribbon enables the dye to be transferred through sublimation effectively by slight heat and prevents welding between the ribbon and print paper by heat.

Description

This invention relates to dye carrier ink ribbons for sublimation transfer type hard copies.
A previously proposed colour copying method employs a dye carrier ink ribbon in which an ink formed by dissolving and dispersing a sublimable dye into a binder resin and solvent is coated on a thin heat-resistant base sheet which may be of paper or the like. The ink ribbon is heated from its reverse side by a thermal print head of a printer to thereby sublimate only the dye contained in the ink, so that the dye is transferred on to printing paper, which is coated on a surface thereof with a resin of excellent dye absorbing capability (such as polyester resin), thereby to form a colour picture image (hard copy).
The dye carrier ink ribbon used in the foregoing colour copying method was required to be capable of efficiently sublimating the dye on to the printing paper, so that the colouring concentration of the picture image is increased to obtain a clear picture image of high contrast, and so that the heat energy that has to be applied to the thermal print heat of the printer is reduced to decrease power consumption and loading of the thermal print head, whereby the life of the thermal print heat is lengthened.
Moreover, the dye carrier ink ribbon used in the foregoing colour copying method is required not only to be capable of efficiently sublimating the dye, but to be such that itwill not be melt bonded by heat to the coating composition coated on the printing paper.
Generally, in the foregoing colour copying method, since the dye contained in the dye carrier ink ribbon is instantaneously sublimated by the thermal print head (which is heated to a high temperature of 200°C or above) and transferred on to the printing paper, which is in contact with the dye carrier ink ribbon, a melt bonding phenomenon easily occurs, according to which the binder resin and dye contained in the ink, and the coating composition coated on the printing paper, are melted by heat and adhere to one another. When this melt bonding occurs, it becomes difficult for the ink ribbon to be released from the printing paper. Particularly in a portion having high colour concentration, the base sheet material is damaged. In addition, the melting phenomenon occurs part by part and, particularly in an intermediate gradation of the picture image, the melt bonding phenomenon appears as a roughness of the picture image. In the case of mixed colours, particularly the concentration of only a portion in which the melted portions are superposed on each other is increased so as thereby to lower the picture quality. As a result, a clear intermediate gradation of the picture could not be obtained. To solve these problems, it has been proposed that the resin contained in the ink be replaced by a resin of sufficiently high heat resistance or that the resin be cured by a curing agent or like means to increase the heat resistance, and that the heat resistance of the printing paper coating composition similarly be increased, thereby to prevent the resins from being melt bonded to each other. However, with the above methods, the resin and dye in the above intermediate gradation cannot sufficiently be prevented from becoming melt bonded to each other. While, as the heat resistance of the resin is increased, it becomes more difficult for the resin covering the dye to be softened by heat generated from the thermal print head upon printing and the probability of the occurrence of the melt bonding phenomenon is reduced, the amount of dye transferred to the printing paper is decreased and the colouring concentration thus is apt to be lowered.
Japanese Patent Application Publication No. JP-A-56/109787 discloses a dye carrier ink ribbon for a sublimation transfer type hard copy, the ink ribbon comprising a heat resistant base sheet and a thermally sublimable ink formed on a surface of the base sheet, the ink comprising a thermally sublimable dye, a binder and powder particles (carbon) of high thermal conductivity and insoluble in a solvent. The binder is a wax and is transferred to printing paper together with the dye upon transfer of the dye.
According to the invention there is provided a dye carrier ink ribbon for a sublimation transfer type hard copy, the ink ribbon comprising a heat resistant base sheet and a thermally sublimable ink formed on a surface of the base sheet, the ink comprising a thermally sublimable dye, a binder and powder particles of high thermal conductivity and insoluble in a solvent, characterised in that the ink comprises 30 to 200 parts by weight of the powder particles dispersed into a total of 100 parts by weight of the dye and binder.
With such an ink ribbon, the sublimable dye can efficiently be sublimated and transferred onto printing paper by heat, and melt bonding between the dye carrier ink ribbon and the printing paper can be avoided.
The invention will now be further described by way of illustrative and non-limiting example.
An ink used in a colour copying method of sublimation transfer type generally is prepared by mixing a sublimable dye and a binder resin containing a curable resin and a solvent, with the addition of a small amount of a dispersion agent and a lubricant. If necessary, for the purposes of improving printing properties and adjusting viscosity, about 10 parts by weight of inorganic fine particles sometimes is added to the ink binder.
The present inventor has found out that a dye carrier ink ribbon, formed by coating on a heat resistant base sheet of paper or the like an ink in which as much as 30 to 200 parts by weight of inorganic powder having excellent thermal conductivity and insoluble to a solvent of the ink are dispersed for 100 parts by weight of the sublimable dye and the binder, is considerably effective for, in particular, the colour copying method. Experimental results proving such effect are described hereinbelow.
First, an ink was formed by mixing 4 parts by weight of Sumikaplast Blue S35 (manufactured by Sumitomo Chemical Co., Ltd.) as a sublimable dye, 6 parts by weight of acetate cellulose (manufactured by Daicel Ltd.) as a binder and 90 parts by weight of methyl ethyl ketone as a solvent. Experiments numbered 1 to 8 were carried out in which silica (Aerosil R972, manufactured by Nippon Aerosil Co., Ltd.) was mixed into the above ink with various mixing ratios within an upper limit of 250 parts by weight relative to a total of 100 parts by weight of the sublimable dye and the binder. In the respective experiments, the mixed compositions were dispersed by a ball mill for one day and coated on a surface of a condenser paper of 25 p thickness so as to have a coating amount of 3 g/m² after being dried, whereby dye carrier ink ribbons were formed. After the inked surface of the dye carrier ink ribbon was put into contact with printing paper which was surface treated in that a surface thereof was coated with polyester resin, the dye carrier ink ribbon was heated at its reverse side by controlling the current of a thermal print head to gradually lower the temperature from a maximum of 300°C so that the amount of dye sublimated was changed and, at the same time, the printing paper and the dye carrier ink ribbon were moved to thereby form a gradation picture image. Then, the melt bonded condition between the ink ribbon and the printing paper and the finished condition of the intermediate gradation after printing were observed. Also, the colouring concentration of cyan at the highest concentration portion of the gradation picture image formed on the printing paper was measured by a Macbeth reflection density meter. The results of Experiment 1 (in which the silica concentration was 0 parts by weight (hereinafter simply described as "silica concentration 0 parts by weight") relative to 100 parts by weight of sublimable dye and acetate cellulose binder), of Experiment 2 (in which the silica concentration was 20 parts by weight), of Experiment 3 (in which the silica concentration was 30 parts by weight), of Experiment 4 (in which the silica concentration was 50 parts by weight), of Experiment 5 (in which the silica concentration was 100 parts by weight), of Experiment 6 (in which the silica concentration was 150 parts by weight), of Experiment 7 (in which the silica concentration was 200 parts by weight) and of Experiment 8 (in which the silica concentration was 250 parts by weight) will now be described with reference to Table 1 below.
In Experiment 1, in which the silica concentration was selected to be 0 parts by weight, the dye carrier ink ribbon and the printing paper were, after printing, completely melt bonded with each other (hereinafter simply described as "melt bonding"). The melt bonding and a roughened finish frequently were found in the finished intermediate gradation of the colouring concentration. Also, it was impossible to measure the cyan colouring concentration (hereinafter simply referred to as the "colouring concentration") of the highest concentration portion of the gradation picture image formed on the printing paper.
In Experiment 2, in which the silica concentration was selected to be 20 parts by weight, the gradation picture image was melt bonded at its high concentration portion, the finished intermediate gradation was frequently roughened and the colouring concentration was 1.31.
In the Experiment 3, in which the silica concentration was selected to be 30 parts by weight, no melt bonding occurred, the finished intermediate gradation was satisfactory and the colouring concentration was 1.65.
In Experiment 4, in which the silica concentration was selected to be 50 parts by weight, no melt bonding occurred, the finished intermediate gradation was satisfactory and the colouring concentration was 1.72.
In Experiment 5, in which the silica concentration was selected to be 100 parts by weight, no melt bonding occurred, the finished intermediate gradation was satisfactory and the colouring concentration was 1.68.
In Experiment 6, in which the silica concentration was selected to be 150 parts by weight, no melt bonding occurred, the finished intermediate gradation was satisfactory and the colouring concentration was 1.65.
In Experiment 7, in which the silica concentration was selected to be 200 parts by weight, no melt bonding occurred, the finished intermediate gradation was satisfactory and the colouring concentration was 1.57.
In Experiment 8, in which the silica concentration was selected to be 250 parts by weight, although no melt bonding occurred, the finished intermediate gradation was poor, the powder partially came off and the colouring concentration was 1.03.
Experiments numbered 9 to 14, in which the mixed particles were not limited to silica but in which other heat conductive powder particles were added, were carried out by the present inventor. These experiments were carried out as follows.
50 parts by weight of various powder particles having excellent heat conductivity were added to 100 parts by weight of the solid components of an ink formed with a mixing ratio of 13 parts by weight of a sublimable dye, namely Kayaset Red 126 (manufactured by Nippon Kayaku Co., Ltd.), 10 parts by weight of ethyl cellulose, 10 parts by weight of melamine resin, 0.2 parts by weight of paratoluenesulphonic acid and 133 parts by weight of methyl ethyl ketone. This product was dispersed for 5 hours by a sand mill treatment and an ink thereby was formed. This ink was coated on rice paper having a weight per unit area of 20 g/m² so as to have a coating weight of 3 g/m² after being dried and thereafter heated for 3 minutes at 80°C and for one hour at 100°C to harden the binder resin whereby a dye carrier ink ribbon was formed. The Experiments 9 to 14, in which the powder particles of excellent heat conductivity to be added were changed and the mixing ratio thereof was changed, were carried out, and experimental results indicated in Table 2 below were obtained. The same terms as those in Table 1 were used for the colouring concentration, the finished intermediate gradation and the melt bonding.
In Experiment 9, in which no powder particles at all were added, the high concentration portion was melt bonded, the finished intermediate gradation was roughened and the colouring concentration was 1.30.
In Experiment 10, in which 50 parts by weight of silica powder only were added, no melt bonding occurred, the intermediate gradation was finished satisfactorily and the colouring concentration was 1.55.
In Experiment 11, in which 50 parts by weight of a mixture of 70% silica powder and 30% carbon powder was added, no melt bonding occurred, the intermediate gradation was finished satisfactorily and the colouring concentration was 1.68.
In Experiment 12, in which 50 parts by weight of a mixture of 70% silica powder and 30% aluminium powder was added, no melt bonding occurred, the intermediate gradation was finished satisfactorily and the colouring concentration was 1.73.
In Experiment 13, in which 50 parts by weight of silicon carbide powder only was added, no melt bonding occurred, the intermediate gradation was finished satisfactorily and the colouring concentration was 1.70.
In Experiment 14, in which a total of 50 parts by weight of silica powder and calcium carbonate with a mixing ratio of 50% and 50% was added, no melt bonding occurred, the intermediate gradation was finished satisfactorily and the colouring concentration was 1.56.
Heat generated by the thermal print head is conducted through the heat-resistant sheet, which forms the base of the ink ribbon, to the ink layer, to heat the dye to its sublimation starting temperature whereby a picture image is formed by sublimating and transferring the dye from the ink ribbon to the surface of the printing paper. The heat generated by the thermal print heat must instantaneously be conducted to the ink layer effectively. From these experiments, it was understood that when the thermally conductive powder particles were dispersed with high concentration in the ink, the heat conducted through the heat resistant sheet was effectively conducted into the ink so as rapidly to start the sublimation of the sublimable dye contained in the ink. The effect cannot be achieved only by increasing the thermal conductivity of the ink ribbon. For example, when a metal foil is used or metallisation is carried out so as to increase the thermal conductivity of the heat resistant sheet, the heat of the thermal print head increasingly is conducted in the lateral direction so that the ink is not heated effectively and the sublimation property of the dye thus is lowered. On the other hand, the powder particles dispersed with high concentration in the inks of the ink ribbons embodying the present invention partially contact each other, whereby, when the particles are dominantly heated, the dye dispersed and adsorbed in the periphery of the particles can effectively be heated and sublimated. However, since the thickness of the ink coating film and the contact area are small, the conduction of heat in the lateral and thickness directions were not much different from each other so that an ink ribbon of excellent sublimation property and of high resolution could be obtained. The above-described advantageous feature of the ink ribbons embodying the present invention can be made more effective if the coating surface of the ink ribbon according to the experimental examples of the present invention is made concave and convex in quite small areas by highly packed powder particles, with the result that the surface area of the ribbon is increased. Accordingly, since a space in which the dye heated by the conducted heat can be sublimated was increased, the amount of dye transferred onto the surface of the printing paper was increased and a picture image of excellent colouring property thus was obtained.
On the other hand, since the formation of such concave and convex portions on the surface of the ink ribbon of the present experimental examples lowers the contact area with the printing paper, there is then an effect that the ink ribbon and the printing paper can be prevented from being melt bonded by heat with each other. Particularly, the heat of the thermal print head was effectively conducted by the powder particles of excellent thermal conductivity packed with high concentration into the ink and the sublimation space was increased by the concave and the convex portions formed on the surface of the ink ribbon to increase the sublimation efficiency so that, even when a heat resistant resin of poor sublimation efficiency as used for the previously proposed ribbon was employed, a picture image of sufficiently high colouring concentration could be formed on the printing paper. As a result, it was found that, in particular, melt bonding on the high concentration portion of the formed picture image was removed and, further, minute melt bonding in the intermediate gradation area could be avoided, whereby a clear image having no scattered dye concentration could be formed over a range from the high concentration area through the intermediate gradation area to th'e low concentration area. From the results of Experiments 1 to 8, it could be confirmed that the above effect could be achieved by dispersing, into a total of 100 parts by weight of the ink binder containing the sublimable dye, 30 to 200 (preferably 40 to 150) parts by weight of powder particles of excellent thermal conductivity insoluble in the solvent. When the amount of power particles added is less than 30 parts by weight, the particles do not contact one another sufficiently and the surface of the ink ribbon is not formed to have quite small concave and convex portions so that the heat cannot be conducted effectively. Also, since the sublimation space is small, the sublimation efficiency cannot be increased sufficiently. In addition, the melt bonding phenomenon between the ink ribbon and the printing paper frequently is caused and, in particular, occurrence of melt bonding on the intermediate gradation area cannot be avoided. When the amount of powder particles added exceeds 200 parts by weight, the powder particles are transferred to the printing paper upon printing, and the dye concentration is reduced too much and the colouring concentration thus becomes insufficient. In this case, the diameter of the powder particles is preferably selected to be less than 100 p, more preferably in a range of from 10 mli to 10 P.
In order to obtain knowledge of the necessary adding ratios of the powder particles, the following . further experiments, numbered 15 to 17, were carried out.
A resin binder comprising a mixture of 10 parts by weight of ethyl cellulose, 10 parts by weight of rapid-curing type melamine resin and 0.2 parts by weight of paratoluenesulphonic acid was mixed with a sublimable dye, namely PS Blue RR (manufactured by Mitsui Toatsu Chemicals, Inc.), so as to provide mixing ratios of the binder to the sublimable dye of 3:1, 3:2 and 3:3. Then, the mixture was diluted by methyl ethyl ketone to 10%.
Powder particles of excellent thermal conductivity, comprising silica powder (Aerosil R972, manufactured by Nippon Aerosil Co., Ltd.) and silicon carbide powder (manufactured by Fujimi Kenmazai Kogyo Kabushiki Kaisha) were mixed with each other with a weight ratio of 3:2, and were added to 100 parts by weight of the ink containing the binder and the dye, which then was dispersed for 15 hours by an attrition mill, whereby an ink was formed. The above ink was coated on condenser paper of a weight per unit area of 20 g/m² in such a manner that the thickness of the ink coating was changed so as to make the dyes in a constant area substantially the same between ink ribbons containing different amount of powder after being dried. Then, ink ribbons were formed and heated at 80°C for 15 hours and the resin was cured. After that, in similar manner to Experiment 1, prints were made on printing paper by using the ink ribbon, and the cyan concentrations of the picture images at their highest concentration portions were measured and compared. In this case, the measured value represented the cyan concentration measured by a Macbeth reflection density meter.
Experiments 15, 16 and 17 will now be described with reference to Table 3 below.
In Experiment 15, in which the mixing ratio of the sublimable dye and the resin was selected to be 1:3, when the added amount of the powder particles relative to 100 parts by weight of the sublimable dye and the resin was selected to be 0 parts by weight, the cyan concentration at the highest concentration portion was 0.98, when it was selected to be 30 parts by weight, the cyan concentration at the highest concentration portion was 1.48, and when it was selected to be 70 parts by weight, the cyan concentration at the highest concentration portion was 1.50.
In Experiment 16, in which the mixing ratio of the sublimable dye and the resin was selected to be 2:3, when the added amount of the powder particles relative to 100 parts by weight of the sublimable dye and the resin was selected to be 0 parts by weight, the cyan concentration at the highest concentration portion was 1.23, when it was selected to be 30 parts by weight, the cyan concentration at the highest concentration portion was 1.60, and when it was selected to be 70 parts by weight, the cyan concentration at the highest concentration portion was 1.65.
In Experiment 17, in which the mixing ratio of the sublimable dye and the resin was selected to be 3:3, when the added amount of the powder particles relative to 100 parts by weight of the sublimable dye and the resin was selected to be 0 parts by weight, the cyan concentration at the highest concentration portion was 1.35, when it was selected to be 30 parts by weight, the cyan concentration at the highest concentration portion was 1.72, and when it was selected to be 70 parts by weight, the cyan concentration at the highest concentration portion was 1.76.
From Experiments 15 to 17, it was understood that, regardless of the mixing ratio of the sublimable dye and the resin, if about 30 parts by weight of powder particles of excellent thermal conductivity were mixed into 100 parts by weight of sublimable dye and resin, satisfactory colouring concentration of the picture image could be obtained.
As will be clear from the various experimental results described above, a dye carrier ink ribbon formed by coating, on a surface of a heat-resistant base sheet, an ink in which 30 to 200 parts by weight of particles of high thermal conductivity and insoluble in a solvent were dispersed into a total of 100 parts by weight of an ink formed of a sublimable dye and a binder, the sublimable dye can efficiently be sublimated and transferred on to printing paper by a small amount of heat and it is possible to prevent the ink ribbon and the printing paper from being melt bonded with each other by heat. The powder particles (of excellent thermal conductivity and insoluble in the solvent) which can be used in the present invention can be inorganic powder particles such as titanium oxide, zinc oxide, calcium carbonate, barium sulphate, aluminium oxide, silica, clay, magnesium oxide, tin oxide, silicon carbide, beryllia, glass powder and the like, and can also be metal powders such as iron powder, copper powder, aluminium powder and the like and carbide such as graphite, carbon and the like. Since these powder particles have high thermal conductivity as compared with the heat resistant plastic sheet or paper which is used as the base material of the ink ribbon, and the resin contained as the binder, the heat conducted from the thermal print heat can effectively be conducted into the ink. In general, if mainly inexpensive inorganic powder particles such as calcium carbonate, clay, silica or the like, and, if necessary, metal powders such as iron powder, aluminium powder and the like and carbon are mixed into the ink, the advantageous effect of the present invention becomes greater. In addition, short fibre-like and phosphor piece-like powders may be added to the ink in a small amount, which does not lower the printing property of the ink.

Claims

1. A dye carrier ink ribbon for a sublimation transfer type hard copy, the ink ribbon comprising a heat resistant base sheet and a thermally sublimable ink formed on a surface of the base sheet, the ink comprising a thermally sublimable dye, a binder and powder particles of high thermal conductivity and insoluble in a solvent, characterised in that the ink comprises 30 to 200 parts by weight of the powder particles dispersed into a total of 100 parts by weight of the dye and binder.

2. A dye carrier ink ribbon according to claim 1, wherein the amount of the powder particles is in a range of from 40 to 150 parts by weight.

3. A dye carrier ink ribbon according to claim 1 or claim 2, wherein the powder particles are selected from titanium oxide, zinc oxide, calcium carbonate, barium sulphate, aluminium oxide, clay, silica, magnesium oxide, tin oxide, silicone carbide, beryllia, glass powder, metal particles, graphite and carbon.

4. A copying method in which a dye carrier ink ribbon according to any one of claims 1 to 3 is brought into contact with printing paper and a picture image is formed on a surface of the printing paper by selectively heating the sublimable dye contained in the ink ribbon.