GB2366392A

GB2366392A - Image-forming substrate

Info

Publication number: GB2366392A
Application number: GB0128644A
Authority: GB
Inventors: Minoru Suzuki
Original assignee: Asahi Kogaku Kogyo Co Ltd
Current assignee: Pentax Corp
Priority date: 1997-08-28
Filing date: 1998-08-27
Publication date: 2002-03-06
Anticipated expiration: 2018-08-27
Also published as: GB2366622B; GB2366622A; GB0128644D0; GB0128645D0; GB2366392B

Abstract

An image-forming substrate 120 comprises:-<BR> ```a sheet of board papers 122;<BR> ```a layer of microcapsules 124, coated over a surface of said board paper sheet, that contains at least one type of microcapsules filled with a dye, said microcapsules exhibiting a temperature/pressure characteristic such that when respective said microcapsules are squashed under a predetermined pressure at a predetermined temperature, said liquid dye seeps from said squashed microcapsule; and<BR> ```a heat-sensitive recording layer 128 formed on another surface of said board paper sheet.

Description

<Desc/Clms Page number 1> IMAGE-FORMING SUBSTRATE The present invention relates to an image-forming substrate coated with a layer of microcapsules filled with dye or ink, on which an image can be formed by selectively breaking or squashing the microcapsules in the layer of microcapsules.

In a conventional type of image-forming substrate coated with a layer of microcapsules filled with dye or ink, a shell of each microcapsule is formed from a suitable photo-setting resin, and an optical image is recorded and formed as a latent image on the layer of microcapsules by exposing it to light rays in accordance with image-pixel signals. Then, the latent image is developed by exerting a pressure on the layer of microcapsules. Namely, the microcapsules which are not exposed to the light rays are broken and squashed whereby the dye or ink seeps out of the broken and squashed microcapsules and thus the latent image is visually developed by the seepage of the dye or ink.

Of course, each of the conventional image-forming substrates must be packed so as to be protected from being exposed to light, resulting in wastage of materials. Further, the image-forming substrates must be handled such that they are not subjected to excess pressure since, due to the softness of unexposed microcapsules, an undesired seepage of the dye or ink can result.

A color-image-forming substrate coated with a layer of icrocapsules filled with different color dyes or inks is also known. In this substrate, the respective different are selectively developed on an image-forming substrate by applying specific temperatures to the layer of color icrocapsules. Nevertheless, for fixing, it is necessary to irradiate a developed color using a light of a specific wavelength. Accordingly, a color- image- forming system for forming a color image on the coior-image forming substrate is costly, because an additional radiation apparatus for the fixing of a developed color is needed, which in turn increases electric power consumption. Also, since the heating process for the color development and the irradiation process for the fixing of a developed color must be carried out with respect to each color, this hinders the quick formation of a color image on the color-image-forming substrate.

Therefore, an object of the present invention is to provide an easy-to-handle image-forming substrate coated with a layer of microcapsules filled with dye or ink, in which an image can be quickly formed on the image-forming substrate at a low cost.

In accordance with a first aspect of the present invention there is provided an image-forming substrate comprising: a base member; and a layer of microcapsules, coated over the base member, that contains at least one type of microcapsules filled with a liquid dye, a shell wall of

each of the microcapsules being composed of a resin that exhibits a temperature/pressure characteristic such that, when each of the microcapsules is squashed under a predetermined pressure at a predetermined temperature, the liquid dye seeps from the squashed microcapsule, wherein a viscosity of the liquid dye varies in accordance a degree of surface roughness of the base member such that the seeped liquid dye securely and finely fixes on the base member.

The base member may comprise a printing paper, and as the degree of surface roughness of the printing paper increases, the viscosity of the liquid dye increases. For example, when the base member comprises an ordinary printing paper exhibiting a high degree of surface roughness, the viscosity of the liquid dye may be approximately 10 cP. Also, when the base member comprises a calendered printing paper exhibiting an intermediate degree of surface roughness, the viscosity of the liquid dye may be approximately 100 cP. Further, when the base member comprises a coated or ferrotype printing paper exhibiting a low degree of surface roughness, and the viscosity of the liquid dye may be approximately 1000 cP.

In accordance with a second aspect of the present invention there is provided an image-forming substrate comprising: a base member; and a layer of transparent microcapsules, coated over the base member, that contains at least one type of transparent microcapsules filled with a transparent liquid dye such a liquid leuco-pigment, a shell

wall of each of the transparent microcapsules being composed of a resin that exhibits a temperature/pressure characteristic such that, when each of the transparent microcapsules is squashed under a predetermined pressure at a predetermined temperature, the transparent liquid dye seeps from the squashed microcapsule and reacts with a transparent color developer to produce a given single color.

In the second aspect of the present invention, the base member may comprise a transparent plastic sheet. In this case, a layer of the transparent color developer is formed on a surface of the transparent plastic sheet formed on a surface thereof, and the transparent microcapsule layer is coated over the transparent color developer layer. Thus, the image- forming substrate can be advantageously utilized to produce a transparency film for an overhead proDector. Optionally, the transparent color developer is contained in a transparent binder solution used to form the transparent microcapsule layer.

Also, in the second aspect of the present invention, the base member may comprise a sheet of paper. In this case, a layer of the transparent color developer is formed on a surface of the paper sheet, and the transparent microcapsule layer is coated over the transparent color developer layer. Thus, when the microcapsuie is broken or compacted, so that a single color is exhibited due to a seepage of the dye or ink from the broken and compacted microcapsule, the exhibited

single color cannot be influenced by the shell of the broken and compacted microcapsule, due to the transparency of the microcapsule shell. Optionally, the transparent color developer may be contained in a binder solution used to form the transparent microcapsule layer.

In accordance with a third aspect of the present invention there is provided an image-forming substrate comprising: a base member; and a layer of microcapsules, coated over the base member, that contains at least one type of microcapsuies filled with a dye, a shell wall of each of the microcapsules being composed of resin that exhibits a temperature/pressure characteristic such that, when each of the microcapsules is squashed under a predetermined pressure at a predetermined temperature, the liquid dye is seeped from the squashed microcapsule, wherein at least one layer of function is incorporated in the image-forming substrate for achieving a given purpose.

The function layer may comprise a sheet of transparent ultraviolet barrier film covering the microcapsule layer. In this case, a preservation of a color image, formed on the image-forming substrate, can be considerably improved due to the existence of the ultraviolet barrier film sheet. Namely, by the ultraviolet barrier film sheet, the formed color image can be prevented from deteriorating due to ultraviolet light. Preferably, the transparent ultraviolet barrier film sheet is covered with a sheet of heat-resistant transparent protective

f ilm.

The function layer may comprise a white coat layer formed on a surface of the base member to give a desired white quality to the surface. In this case, the microcapsule layer is formed over the surface of the white coat layer. Also, the function layer may comprise an electrical conductive layer formed on another surface of the base member.

In the third aspect of the present invention, the base member may comprise a sheet of paper, and the function layer may comprise a layer of adhesive formed on another surface of the paper sheet, and a sheet of release paper applied to the adhesive layer. In this case, the image-forming substrate is produced in a form of a sea! sheet, a piece of which may be utilized as a seal adapted to be adhered to a post card, an envelop, a package or the like.

The base member may comprise a sheet of film composed of a suitable synthetic resin, and the function layer may comprise a peeling layer formed over a surface of the film sheet, and a layer of transparent ultraviolet barrier formed on the peeling layer. In this case, the image-forming substrate is produced in a form of a transfer film sheet, and is used together with a printing sheet of paper. Namely, an image is once formed on the transfer film sheet, and is then transferred from the transfer film sheet to the printing paper sheet. Further, a preservation of the transferred image can be considerably improved because the transferred image is

coated with a thermally-fused transparent material, derived from the ultraviolet barrier layer.

The base member also may comprise a sheet of film composed of a suitable transparent synthetic resin, and the function layer may comprise a peeling layer formed on a surface of the transparent film sheet, and a layer of transparent ultraviolet barrier formed on the peeling layer, the microcapsule layer being coated over the transparent ultraviolet barrier layer. In this case, the image-forming substrate is also produced in a form of a transfer film sheet, and is used together with a printing sheet of paper. Similar to the above-mentioned transfer film sheet, an image is once formed on the transfer film sheet, and is then transferred from the transfer film sheet to the printing paper sheet. Nevertheless, after the transfer of the image from the transfer film sheet to the printing paper sheet, the remaining transfer film sheet can be utilized as a transparency film carrying a negative image. Also, a preservation of the transferred image can be considerably improved because the transferred image is coated with a thermally-fused transparent material, derived from the ultraviolet barrier layer.

The base member may comprise a sheet of board paper, and the function layer may comprise a heat-sensitive recording layer formed on another surface of the board paper sheet. In this case, the image-forming substrate can be advantageously utilized as a post card.

The base member may comprise a sheet composed of a suitable transparent synthetic resin, and the function layer may comprise a heat-sensitive recording layer formed on another surface of the transparent sheet. In this case, the heat-sensitive recording layer is used for producing a black dot on the image-forming substrate.

In accordance with a fourth aspect of the present invention there is provided an image-forming substrate which is produced in a form of a duplicating-paper sheet or a double-recording-paper sheet. Namely, the image-forming substrate comprises: a first image-forming substrate element that includes a first sheet of paper and a first layer of microcapsules coated over a surface of the first paper sheet, the first microcapsule layer containing at least one type of microcapsules filled with a dye, a shell of wall of each of the microcapsuies being composed of a resin that exhibits a temperature/pressure characteristic such that, when each of the microcapsules is squashed under a first predetermined pressure at a first predetermined temperature, the dye seeps from the squashed microcapsule; a second image-forming substrate element that includes a second sheet of paper and a second layer of microcapsules coated over a surface of the second paper sheet, the second microcapsule layer containing at least one type of microcapsules filled with a dye, a shell of wall of each of the microcapsules being composed of a resin that exhibits a temperature/pressure characteristic such that,

when each of the microcapsules is squashed under a second predetermined pressure at a second predetermined temperature, the dye seeps from the squashed microcapsule; and an peeling layer interposed between the first and second image-forming substrate elements, wherein the first and second predetermined pressures and the first and second predetermined temperatures are simultaneously applied to the first and second image- forming substrate elements, and the second image-forming substrate is peelable from the peeling layer.

In the above-mentioned aspects of the present invention, the resin of the shell wall may be a shape memory resin that exhibits a glass-transition temperature corresponding to the predetermined temperature.

Optionally, the shell wall may comprise a double-shell wall. In this case, one shell wall element of the double- shell wall is composed of a shape memory resin, and another shell wall element of the double-shell wall is composed of a resin not exhibiting a shape memory characteristic, such that the temperature/pressure characteristic is a resultant temperature/pressure characteristic of both the shell wall elements.

Also, the shell wall may comprise a composite-shell wall including at least two shell wall elements formed of different types of resin not exhibiting a shape memory characteristic, such that the temperature/pres sure characteristic is a resultant temperature/pressure characteristic of the shell

wall elements.

The object and other objects of the present invention will be better understood from the following description, with reference to the accompanying drawings in which: Figure 1 is a schematic conceptual cross sectional view showing a first embodiment of an image-forming substrate, of the present invention, comprising a layer of microcapsules including a first type of cyan microcapsules filled with a cyan ink, a second type of magenta microcapsules filled with a magenta ink and a third type of yellow microcapsules filled with a yellow ink; Figure 2 is a graph showing a characteristic curve of a longitudinal elasticity coefficient of a shape memory resin; Figure 3 is a graph showing temperature/pressure breaking characteristics of the respective cyan, magenta and yellow microcapsules shown in Fig. 1, with respective hatched areas indicating each of a cyan-producing area, a magenta-producing area and a yellow-producing area; Figure 4 is a schematic cross-sectional view showing different shell wall thicknesses of the respective cyan, magenta and yellow microcapsules shown in Fig. 1; Figure 5 is a schematic conceptual cross-sectional view similar to Fig. 1, showing only a selective breakage of one of the cyan microcapsules in the layer of microcapsuies; Figure 6 is a schematic cross-sectional view of a color printer for forming a color image on the image-forming

substrate shown in Fig. 1; Figure 7 is a partial schematic block diagram of three line-type thermal heads and three driver circuits therefor incorporated in the color printer of Fig. 6; Figure 8 is a schematic block diagram of a control board of the color printer shown in Fig. 6; Figure 9 is a partial block diagram representatively showing a set of an AND-gate circuit and a transistor included in each of the thermal head driver circuits of Figs. 7 and 8; Figure 10 is a timing chart showing a strobe signal and a control signal for electronically actuating one of the thermal head driver circuits for producing a cyan dot on the image- forming substrate of Fig. 1; Figure 11 is a timing chart showing a strobe signal and a control signal for electronically actuating another one of the thermal head driver circuits for producing a magenta dot on the image-forming substrate of Fig. 1; Figure 12 is a timing chart showing a strobe signal and a control signal for electronically actuating the remaining thermal head driver circuit for producing a yellow dot on the image-forming substrate of Fig. 1; Figure 13 is a conceptual view showing, by way of example, the production of color dots of a color image in the color printer of Fig. 6; Figure 14 is a schematic conceptual cross-sectional view showing a second embodiment of an image-forming substrate, of

the present invention, comprising a layer of microcapsules including a first type of microcapsules filled with a first transparent liquid leuco-pigment, a second type of microcapsules filled with a second transparent liquid leuco- pigment, and a third type of microcapsules filled with a third transparent liquid leuco-pigment; Figure 1S is a schematic cross-sectional view showing different shell wall thicknesses of the respective first, second and third types of microcapsules shown in Fig. 14; Figure 16 is a schematic conceptual cross-sectional view similar to Fig. 14, showing a modification of the second embodiment of the image-forming substrate of the present invention; Figure 17 is a schematic conceptual cross-sectional view showing a third embodiment of an image-forming substrate of to the present invention; Figure 18 is a schematic conceptual cross sectional view showing a fourth embodiment of an image-forming substrate of the present invention; Figure 19 is a schematic conceptual cross-sectional view showing a fifth embodiment of an image-forming substrate of the present invention; Figure 20 is a schematic conceptual cross-sectional view showing the image-forming substrate of Fig. 19 together with a printing sheet of paper.to which a color image should be transferred from the image-forming substrate of Fig. 19;

Figure 21 is a schematic conceptual cross-sectional view similar to Fig. 20 showing a modification of the fifth embodiment of the image-forming substrate shown in Fig. 19; Figure 22 is a schematic conceptual cross-sectional view showing a sixth embodiment of an image-forming substrate of the present invention; Figure 23 is a schematic conceptual cross-sectional view showing the image-forming substrate of Fig. 22 together with a printing sheet of paper to which a color image should be transferred from the image-forming substrate of Fig. 22; Figure 24 is a schematic conceptual cross-sectional view similar to Fig. 23 showing a modification of the sixth embodiment of the image-forming substrate shown in Fig. 22; Figure 25 is a schematic conceptual cross-sectional view showing a seventh embodiment of an image-forming substrate of the present invention; Figure 26 is a schematic conceptual cross-sectional view showing an eighth embodiment of an image-forming substrate of the present invention; Figure 27 is a schematic conceptual cross-sectional view showing a ninth embodiment of an image-forming substrate of the present invention; Figure 28 is a graph showing temperature/pressure breaking characteristics of respective cyan, magenta and yellow microcapsules included in a second microcapsule layer shown in Fig. 27;

Figure 29 is a schematic conceptual cross-sectional view showing the ninth embodiment of the image-forming substrate of Fig. 27 peeled into two elements; Figure 30 is a schematic conceptual cross-sectional view showing a tenth embodiment of an image-forming substrate of the present invention; Figure 31 is a schematic conceptual cross-sectional view showing the tenth embodiment of the image-forming substrate of Fig. 30 peeling into two elements; Figure 32 is a cross-sectional view showing three types of cyan, magenta and yellow microcapsules, respectively, for use as the microcapsule in the present invention; Figure 33 is a graph showing temperature/pressure breaking characteristics of the cyan, magenta and yellow microcapsules shown in Fig. 32; Figure 34 is a cross-sectional view showing three types of cyan, magenta and yellow microcapsules, respectively, for use as the microcapsule in the present invention; Figure 35 is a graph showing temperature/pressure breaking characteristics of the cyan, magenta and yellow microcapsules shown in Fig. 34; and Figure 36 is a schematic plan view showing a further embodiment of an image-forming substrate of the present invention.

Figure 1 shows a first embodiment of an image-forming substrate, generally indicated by reference 10, of the present

invention. In this first embodiment, the image-forming substrate 10 is produced in the form of a paper sheet. In particular, the image-forming substrate 10 comprises a sheet of paper 12, a layer of microcapsules 14 coated over a surface of the sheet of paper 12, and a sheet of transparent protective film 16 covering the microcapsule layer 14.

The microcapsule layer 14 is formed from three types of microcapsules: a first type of microcapsules 18C filled with cyan liquid dye or ink, a second type of microcapsules 18M filled with magenta liquid dye or ink, and a third type of microcapsules 18Y filled with yellow liquid dye or ink. These three types of microcapsules are uniformly distributed in the microcapsule layer 14. In each type of microcapsule (18C, 18M, 18Y), a shell of a microcapsule is formed of a synthetic resin material, usually colored white. Also, each type of microcapsule (18C, 18M, 18Y) may be produced by a well-known polymerization method, such as interfacial polymerization, in- situ polymerization or the like, and may have an average diameter of several microns, for example, 5pm to 10#m.

Note, when the sheet of paper 12 is colored with a single color pigment, the resin material of the microcapsules 18C, 18M and 18Y may be colored with the same single color pigment.

For the uniform formation of the layer of microcapsules 14, for example, the same amounts of cyan, magenta and yellow microcapsules 18C, 18M and 18Y are homogeneously mixed with a suitable binder solution to form a suspension, and the sheet

of paper 12 is coated with the binder solution containing the suspension of microcapsules 18C, 18M and 18Y by using an atomizer. In Fig. 1, for the convenience of illustration, although the layer of microcapsules 14 is shown as having a thickness corresponding to the diameter of the microcapsules 18C, 18M and 18Y, in reality, the three types of microcapsules 18C, 18M and 18Y overlay each other, and thus the layer of microcapsules 14 has a larger thickness than the diameter of a single microcapsule 18C, 18M or 18Y.

In the first embodiment of the image-forming substrate 10, for the resin material of each type of microcapsule (18C, 18M, 18Y), a shape memory resin is utilized. For example, the shape memory resin is represented by a polyurethane-based- resin, such as polynorbornene, trans-1, 4-polyisoprene polyurethane. As other types of shape memory resin, a polyimide-based resin, a polyamide-based resin, a polyvinyl- chloride-based resin, a polyester-based resin and so on are also known. In general, as shown in a graph of Fig. 2, the shape memory resin exhibits a coefficient of longitudinal elasticity, which abruptly changes at a glass-transition temperature boundary T9, In the shape memory resin, Brownian motion of the molecular chains is stopped in a low-temperature area "a", which is less than the glass- transition temperature T., and thus the shape memory resin exhibits a glass-like phase, i.e. the chains are relatively fixed. On the other

hand, Brownian movement of the molecular chains becomes increasingly energetic in a high-temperature area "b", which is higher than the glass-transition temperature Tg, and thus the shape memory resin exhibits a rubber elasticity, i.e. the chains are relatively flexible.

The shape memory resin is named due to the following shape memory characteristic: after a mass of the shape memory resin is worked into a shaped article in the low-temperature area "a", when such a shaped article is heated over the glass- transition temperature Tg, the article becomes freely deformable. After the shaped article is deformed into another shape, when the deformed article is cooled to below the glass- transition temperature Tg, the other shape of the article is fixed and maintained. Nevertheless, when the deformed article is again heated to above the glass-transition temperature T., without being subjected to any load or external force, the deformed article returns to the original shape.

In the image-forming substrate or sheet 10 of the present invention, the shape memory characteristic per se is not utilized, but the characteristic abrupt change of the state of the memory resin, i.e. in the longitudinal elasticity coefficient, is utilized such that the three types of microcapsules 18C, 18M and 18Y can be selectively squashed and broken at different temperatures and under different pressures, respectively.

As shown in a graph of Fig. 3, a shape memory resin of

the cyan microcapsules 18C is prepared so as to exhibit a characteristic longitudinal elasticity coefficient having a glass-tran5ition temperature T1, indicated by a solid line; a shape memory resin of the magenta microcapsules 18M is prepared so as to exhibit a characteristic longitudinal elasticity coefficient having a glass-transition temperature T2, indicated by a single-chained line; and a shape memory resin of the yellow microcapsules 18Y is prepared so as to exhibit a characteristic longitudinal elasticity coefficient having a glass-transition temperature T3, indicated by a double-chained line.

By suitably varying compositions of the shape memory resin and/or by selecting a suitable one from among various

types of shape memory resin, it is possible to obtain the respective shape memory resins, with the glass-transition temperatures T1, T2 and T3- For example, the respective glass-transition temperatures T1, T2 and T3 may be 700C, 1100C and 130'C. As shown in Fig. 4, the microcapsule walls of the cyan microcapsules 18C, magenta microcapsules 18M, and yellow microcapsules 18Y, respectively, have differing thicknesses WCI WM and Wy. The thickness WC of cyan microcapsules 18C is larger than the thickness WM of magenta microcapsules 18M, and the thickness WM of magenta microcapsules 18M is larger than the thickness Wy of yellow microcapsuies 18Y.

The wall thickness WC of the cyan microcapsules 18C is

selected such that each cyan microcapsule 18C is compacted and broken under a breaking pressure that lies between a critical breaking pressure P3 and an upper limit pressure PUL (Fig. 3), when each cyan microcapsule 18C is heated to a temperature between the glass-transition temperatures T, and T2; the wall thickness WM of the magenta microcapsules 18M is selected such that each magenta microcapsule 18M is compacted and broken under a breaking pressure that lies between a critical breaking pressure P2 and the critical breaking pressure P3 (Fig. 3), when each magenta microcapsule 18M is heated to a temperature between the glass-transition temperatures T2 and T3; and the wall thickness Wy of the yellow microcapsules 18Y is selected such that each yellow microcapsule 18Y is compacted and broken under a breaking pressure that lies between a critical breaking pressure P, and the critical breaking pressure P2 (Fig. 3), when each yellow microcapsule 18Y is heated to a temperature between the glass-transition temperature T3 and an upper limit temperature TUL- Note, the upper limit pressure PUL and the upper limit temperature TUL are suitably set in view of the characteristics of the used shape memory resins.

As is apparent from the foregoing, by suitably selecting a heating temperature and a breaking pressure, which should be exerted on the image-forming sheet 10, it is possible to selectively break and squash the cyan, magenta and yellow microcapsules 18C, 18M and 18Y.

For example, if the selected heating temperature and breaking pressure fall within a hatched cyan area C (Fig. 3), defined by a temperature range between the glass-transition temperatures T, and T2 and by a pressure range between the critical breaking pressure P3 and the upper limit pressure PUL, only the cyan microcapsules 18C are squashed and broken, as shown in Fig. 5. Also, if the selected heating temperature and breaking pressure fall within a hatched magenta area M, defined by a temperature range between the glass-transition temperatures T2 and T3 and by a pressure range between the critical breaking pressures P2 and P3, only the magenta microcapsules 18M are squashed and broken. Further, if the selected heating temperature and breaking pressure fall within a hatched yellow area Y, defined by a temperature range between the glass-transition temperature T3 and the upper limit temperature TUL and by a pressure range between the critical breaking pressures P, and P2, only the yellow microcapsules 18Y are squashed and broken.

Accordingly, if the selection of a heating temperature and a breaking pressure, which should be exerted on the image- forming sheet 10, are suitably controlled in accordance with digital color image-pixel signals (digital cyan image-pixel signals, digital magenta image-pixel signals and digital yellow image-pixel signals), it is possible to form a color image on the image-forming sheet 10 on the basis of the digital color image-pixel signals.

Figure 6 schematically shows a thermal color printer, which is constituted as a line printer so as to form a color image on the image-forming sheet 10.

The color printer comprises a rectangular parallelopiped housing 20 having an entrance opening 22 and an exit opening 24 formed in a top wall and a side wall of the housing 20, respectively. The image-forming sheet 10 is introduced into the housing 20 through the entrance opening 22, and is then discharged from the exit opening 24 after the formation of a color image on the image-forming sheet 10. Note, in Fig. 6, a path 26 for movement of the image-forming sheet 10 is indicated by a chained line.

A guide plate 28 is provided in the housing 20 so as to define a part of the path 26 for the movement of the image- forming sheet 10, and a first thermal head 30C, a second thermal head 30M and a third thermal head 30Y are securely attached to an upper surface of the guide plate 28. Each thermal head (30C, 30M, 30Y) is formed as a line thermal head perpendicularly extending with respect to the direction of the movement of the image-forming sheet 10.

As shown in Fig. 7, the line thermal head 30C includes a plurality of heater elements or electric resistance elements Rc, to Rcn, and these resistance elements are aligned with each other along a length of the line thermal head 30C. The electric resistance elements R.1 to Rcn are selectively energized by a first driver circuit 31C in accordance with a

single-line of cyan image-pixel signals, and are then heated to a temperature between the glass-transition temperatures T, and T2- The line thermal head 30M also includes a plurality of heater elements or electric resistance elements Rm, to Rmn, and these resistance elements are aligned with each other along a length of the line thermal head 30M. The electric resistance elements Rmi to Rmn are selectively energized by a second driver circuit 31M in accordance with a single-line of magenta image-pixel signals, and are then heated to a temperature between the glass-transition temperatures T2 and T3- Further, the line thermal head 30Y includes a plurality of heater elements or electric resistance elements RY1 to Ryn/ and these resistance elements are aligned with each other along a length of the line thermal head 30Y. The electric resistance elements Ryl to Ryn are selectively energized by a third driver circuit 31Y in accordance with a single-line of yellow image-pixel signals, and are heated to a temperature between the glass-transition temperature T3 and the upper limit temperature TUL- Namely, the line thermal heads 30C, 30M and 30Y are arranged in sequence so 'Ehat the respective heating temperatures increase in the movement direction of the image- forming substrate 10.

The color printer further comprises a first roller platen

32C, a second roller platen 32M and a third roller platen 32Y associated with the first, second and third thermal heads 30C, 30M and 30Y, respectively. Each of the roller platens 32C, 32M and 32Y is formed of a suitable hard rubber material. The first roller platen 32C is provided with a first spring- biasing unit 34C so as to be elastically pressed against the first thermal head 30C at a pressure between the critical breaking-pressure P3 and the upper limit pressure PUL; the second roller platen 32M is provided with a second spring- biasing unit 34M so as to be elastically pressed against the second thermal head 30M at a pressure between the critical breaking-pressures P2 and P3; and the third roller platen 32Y is provided with a third spring-biasing unit 34Y so as to be elastically pressed against the second thermal head 30Y at a pressure between the critical breaking-pressures P, and P2.

Namely, the platens 32C, 32M and 32Y are arranged in sequence so that the respective pressures, exerted by the platens 32C, 32M and 32Y on the line thermal heads 30C, 30M and 30Y, decrease in the movement direction of the image- forming substrate 10.

Note, in Fig. 6, reference 36 indicates a control circuit board for controlling a printing operation of the color printer, and reference 38 indicates an electrical main power source for electrically energizing the control circuit board 36.

Figure 8 shows a schematic block diagram of the control

circuit board 36. As shown in this drawing, the control circuit board 36 comprises a central processing unit (CPU) 40, which receives digital color image-pixel signals from a personal computer or a word processor (not shown) through an interface circuit (I/F) 42, and the received digital color image-pixel signals, i.e. digital cyan image-pixel signals, digital magenta image-pixel signals and digital yellow image- pixel signals, are stored in a memory 44.

Also, the control circuit board 36 is provided with a motor driver circuit 46 for driving three electric motors 48C, 48M and 48Y, which are used to rotate the roller platens 32C, 32M and 32Y, respectively. In this printer, each of the motors 48C, 48M and 48Y is a stepper motor, which is driven in accordance with a series of drive pulses outputted from the motor driver circuit 46, the outputting of drive pulses from the motor driver circuit 46 to the motors 48C, 48M and 48Y being controlled by the CPU 40.

During a printing operation, the respective roller platens 32C, 32M and 32Y are rotated in a counterclockwise direction (Fig. 6) by the motors 48C, 48M and 48Y, respectively, with the same peripheral speed. Accordingly, the image-forming sheet 10, introduced through the entrance opening 22, moves toward the exit opening 24 along the path 26. Thus, the image-forming sheet 10 is subjected to pressure ranging between the critical breaking-pressure P3 and the upper limit pressure PUL when passing between the first line

thermal head 30C and the first roller platen 32C; the image- forming sheet 10 is subjected to pressure ranging between the critical breaking-pressures P2 and P3 when passing between the second line thermal head 30M and the second roller platen 32M; and the image-forming sheet 10 is subjected to pressure ranging between the critical brea king-pre s sure s P, and P2 when passing between the third line thermal head 30Y and the third roller platen 32Y.

Note, in this embodiment, the introduction of the image- forming sheet 10 into the entrance opening 22 of the printer is carried out such that the transparent protective film sheet 16 of the image-forming sheet 10 comes into contact with the thermal heads 30C, 30M and 30Y.

As is apparent from Fig. 8, the respective driver circuits 31C, 31M and 31Y for the line thermal heads 30C, 30M and 30Y are controlled by the CPU 40. Namely, the driver circuits 31C, 31M and 31Y are controlled by n sets of strobe signals "STC" and control signals "DAC", n sets of strobe signals "STM" and control signals "DAM", and n sets of strobe signals "'STY" and control signals "DAY", respectively, thereby carrying out the selective energization of the electric resistance elements R.1 to Rcn, the selective energization of the electric resistance elements Rml to Rmn and the selective energization of the electric resistance elements Ryl to Ryn, as stated in detail below.

In each driver circuit (31C, 31M and 31Y) , n sets of AND-

gate circuits and transistors are provided with respect to the electric resistance elements (Rcnl Rmn, Ryn) , respectively. With reference to Fig. 9, an AND-gate circuit and a transistor in one set are representatively shown and indicated by references 50 and 52, respectively. A set of a strobe signal (STC, STM or STY) and a control signal (DAC, DAM or DAY) is inputted from the CPU 40 to two input terminals of the AND- gate circuit 50. The base of the transistor 52 is connected to an output terminal of the AND-gate circuit 50; the collector of the transistor 52 is connected to an electric power source (Vcc) ; and the emitter of the transistor S2 is connected to a corresponding electric resistance element (Rcnf Rmn, Ryn)- When the AND-gate circuit SO, as shown in Fig. 9, is one included in the first driver circuit 31C, a set of a strobe signal "STC" and a control signal "DAC" is inputted to the input terminals of the AND-gate circuit 50. As shown in a timing chart of Fig. 10, the strobe signal "STC" has a pulse width "PWC". On the other hand, the control signal "DAC" varies in accordance with binary values of a digital cyan image-pixel signal. Namely, when the digital cyan image-pixel signal has a value "l", the control signal "DAC" produces a high-level pulse having the same pulse width as that of the strobe signal "STC", whereas, when the digital cyan image- pixel signal has a value "0", the control signal "DAC"' is maintained at a low-level.

Accordingly, only when the digital cyan image-pixel signal has the value "1", is a corresponding electric resistance element (Rcl, ..., Rcn) electrically energized during a period corresponding to the pulse width "'PWC" of the strobe signal "STC", whereby the electric resistance element concerned is heated to the temperature between the glass- transition temperatures T, and T2, resulting in the production of a cyan dot on the image-forming sheet 10 due to the compacting and breakage of cyan microcapsules 18C, which are locally heated by the electric resistance element concerned.

Similarly, when the AND-gate circuit 50, as shown in Fig. 9, is one included in the second driver circuit 31M, a set of a strobe signal "STM" and a control signal "DAM" is inputted to the input terminals of the AND-gate circuit 50. As shown in a timing chart of Fig. 11, the strobe signal "STM" has a pulse width "PWM"', being longer than that of the strobe signal "STC". On the other hand, the control signal "DAM" varies in accordance with binary values of a digital magenta image-pixel signal. Namely, when the digital magenta image-pixel signal has a value "1", the control signal "DAM produces a high- level pulse having the same pulse width as that of the strobe signal "STM", whereas, when the digital magenta image-pixel signal has a value "0", the control signal "DAM" is maintained at a low-level.

Accordingly, only when the digital magenta image-pixel signal is "1", is a corresponding electric resistance element

(Rml, -, Rmn) electrically energized during a period corresponding to the pulse width "PWM" of the strobe signal "STM", whereby the electric resistance element concerned is heated to the temperature between the glass-transition temperatures T2 and T3, resulting in the production of a magenta dot on the image-forming sheet 10 due to the compacting and breakage of magenta microcapsules 18M, which are locally heated by the electric resistance element concerned.

Further, when the AND-gate circuit 50, as shown in Fig. 9, is one included in the first driver circuit 31Y, a set of a strobe signal "STY" and a control signal "DAY" is inputted to the input terminals of the AND-gate circuit SO. As shown in a timing chart of Fig. 12, the strobe signal "STY"' has a pulse width "PWY"', being longer than that of the strobe signal "STM". On the other hand, the control signal "DAY" varies in accordance with binary values of a corresponding digital yellow image-pixel signal. Namely, when the digital yellow image-pixel signal has a value "1", the control signal "DAY" produces a high-level pulse having the same pulse width as that of the strobe signal "STY", whereas, when the digital yellow image-pixel signal has a value "0", the control signal "DAY" is maintained at a low-level.

Accordingly, only when the digital yellow image-pixel signal is "1", is a corresponding electric resistance element (Ryl, -, Ryn) electrically energized during a period

corresponding to the pulse width "PWY" of the strobe signal "STY", whereby the resistance element concerned is heated to the temperature between the glass-transition temperature T3 and the upper limit temperature TUL, resulting in the production of a yellow dot on the image-forming sheet 10 due to the compacting and breakage of yellow microcapsules 18Y, which are locally heated by the electric resistance element concerned.

Note, the cyan, magenta and yellow dots, produced by the heated resistance elements Rcn, Rmn and Ryn, have a dot size of about 50 pm to about 100 pm, and thus three types of cyan, magenta and yellow microcapsules 18C, 18M and 18Y are uniformly included in a dot area to be produced on the image- forming sheet 10.

Of course, the color image is formed on the image-forming sheet 10 on the basis of a plurality of three-primary color dots obtained by selectively heating the electric resistance elements (Rc, to Rcn; Rm, to Rmn; and Ryl to Ryn) in accordance with three-primary color digital image-pixel signals. Namely, a certain dot of the color image, formed on the image-forming sheet 10, is obtained by a combination of cyan, magenta and yellow dots produced by corresponding electric resistance elements Rcn, Rmn and Ryn- In particular, for example, as conceptually shown by Fig. 13, in a single-line of dots, forming a part of the color image, if a first dot is white, none of the electric

resistance elements RC11 Rm, and Ry, are heated. If a second dot is cyan, only the electric resistance element R.2 is heated, and the remaining electric resistance elements Rm2 and Ry2 are not heated. If a third dot is magenta, only the resistance element Rm3 is heated, and the remaining resistance elements R.3 and Ry3 are not heated. Similarly, if a fourth dot is yellow, only the resistance element Ry4 is heated, and the remaining resistance elements Rc4 and Rm4 are not heated.

Further, as shown in Fig. 13, if a fifth dot is blue, the electric resistance elements Rc5 and RmS are heated, and the remaining electric resistance element RyS is not heated. If a sixth dot is green, the resistance elements R.6 and Ry6 are heated, and the remaining resistance element Rm6 is not heated. If a seventh dot is red, the resistance elements Rm7 and Ry7 are heated, and the remaining resistance element R.7 is not heated. If an eighth dot is black, all of the resistance elements RC8f RmB and RyS are heated.

According to the first embodiment of the image-forming substrate 10, a viscosity of each of the cyan, magenta and yellow liquid dyes or inks is changed in accordance with a degree of surface roughness of the sheet of paper 12 used, such that a produced dot can be securely and finely fixed on the sheet of paper 12.

In particular, for example, when an ordinary printing paper, exhibiting a high degree of surface roughness, is used as the sheet of paper 12 in the image-forming substrate 10,

each of the cyan, magenta and yellow liquid dyes or inks is prepared so as to exhibit a relatively low viscosity, for example, 10 cp (centipoise) at the temperature at which the corresponding monochromatic microcapsules (18C, 18M, 18Y) are compacting and broken. In this case, the liquid dye or ink, which seeps out of the compacted and broken microcapsules, immediately permeates the tissue of the ordinary printing paper 12, and thus can be securely fixed on the ordinary printing paper due to the immediate permeation of the discharged liquid dye or ink into the tissue thereof. Thus, a dot can be finely and definitely produced on the ordinary printing paper 12 by the seeped liquid dye or ink.

When instead a calendered printing paper, exhibiting an intermediate degree of surface roughness, is used as the sheet of paper 12 in the image-forming substrate 10, each of the cyan, magenta and yellow liquid dyes or inks is prepared so as to exhibit an intermediate viscosity, for example, 100 cp at the temperature at which the corresponding monochromatic microcapsules (18C, 18M, 18Y) are compacted and broken. In this case, the liquid dye or ink, which seeps out of the compacted and broken microcapsules, cannot immediately permeate the tissue of the calendered printing paper. However, the discharged liquid dye or ink can be securely fixed on the calendered printing paper 12 without spreading of the seeped liquid dye or ink due to the intermediate viscosity thereof. Thus, a dot can be finely and definitely produced on the

calendered printing paper 12 by the seeped liquid dye and ink. Further, when a coated or ferrotype printing paper, exhibiting a relatively low degree of surface roughness, is used as the sheet of paper 12 in the image-forming substrate 10, each of the cyan, magenta and yellow liquid dyes or inks is prepared so as to exhibit a relatively high viscosity, for example, 1000 cp at the temperature at which the corresponding monochromatic microcapsules (18C, 18M, 18Y) are compacted and broken. In this case, the liquid dye or ink, which seeps out of the compacted and broken micrccapsules, does not quickly permeate the tissue of the coated or ferrotype printing paper 12. However, the discharged liquid dye or ink can be securely fixed on the coated or ferrotype printing paper 12 without spreading of the seeped liquid dye or ink due to the high viscosity thereof. Thus, a dot can be finely and definitely produced on the coated or ferrotype printing paper 12 by the seeped liquid dye and ink.

Figure 14 shows a second embodiment of an image-forming substrate, generally indicated by reference 54, of the present invention. In this second embodiment, the image-forming substrate 54 is produced in the form of a transparent sheet. In particular, the image-forming substrate 54 comprises a sheet 56 of a suitable transparent resin, a layer of transparent color developer 58 formed on a surface of the transparent sheet 56, a layer of transparent microcapsules 60 coated over a surface of the transparent color developer layer

58, and a sheet of transparent protective film 62 covering the microcapsule layer 58.

The transparent microcapsule layer 60 is formed from three types of microcapsules: a first type of microcapsules 64C filled with a first transparent liquid leuco-pigment, a second type of microcapsules 64M filled with a second transparent liquid leuco-pigment, and a third type of microcapsules 64Y filled with a third transparent liquid leuco-pigment. The respective first, second and third liquid leuco-pigments react with the color developer, included in the color developer layer 58, to thereby produce cyan, magenta and yellow.

Similar to the first embodiment, for the resin material of each type of microcapsule (64C, 64M, 64Y), a shape memory resin is utilized, but it is transparent. of course, the microcapsules 64C, 64M and 64Y, which are filled with leuco- pigments, are produced by one of the well-known polymerization methods mentioned above.

The microcapsules 64C, 64M and 64Y are uniformly distributed in the microcapsule layer 60. To this end, for example, similar to the first embodiment, the same amounts of cyan, magenta and yellow microcapsules 64C, 64M and 64Y are homogeneously mixed with a suitable transparent binder solution to form a suspension, and the transparent sheet 56 is coated with the binder solution, containing the suspension of microcapsules 64C, 64M and 64Y, by using an atomizer. Also,

similar to Fig. 1, in Fig. 14, for the convenience of illustration, although the microcapsule layer 60 is shown as having a thickness corresponding to the diameter of the microcapsules 64C, 64M and 64Y, in reality, the three types of microcapsules 64C, 64M and 64Y overlay each other, and thus the microcapsule layer 60 has a larger thickness than the diameter of a single microcapsule 64C, 64M or 64Y.

Further, similar to the first embodiment, the cyan microcapsules 64C, magenta microcapsules 64M, and yellow microcapsules 64Y, respectively, have differing thicknesses WcI WM and Wy, as shown in Fig. 15. Namely, the thickness WC of cyan microcapsules 64C is 'Larger than the thickness WM of magenta microcapsules 64M, and the thickness WM of magenta microcapsules 64M is larger than the thickness Wy of yellow microcapsules 64Y.

Accordingly, the respective microcapsules 64C, 64M and 64Y also exhibit the temperature/pressure charac-teristics, as shown in Fig. 3. Namely, by suitably selecting a heating temperature and a breaking pressure, which should be exerted on the image-forming substrate 54, it is possible to selectively compact and break the cyan, magenta and yellow microcapsules 64C, 64M and 64Y, and thus a color image can be formed on the image-forming substrate 54 by the thermal color printer as shown in Fig. 6.

The second embodiment of the transparency i'mage-forming substrate of the present invention can be especially

advantageously utilized to produce a transparency film for a well-known overhead projector (OHP). Namely, when a color image is formed on the image-forming substrate 54, it is possible to directly use this transparency-type substrate 54, carrying the color image, as a transparency film for the overhead projector.

Figure 16 shows a modification of the second embodiment of the image-forming substrate of the present invention generally indicated by reference 541. In the modified image- forming substrate 541, a sheet of paper 561 is substituted for the transparent sheet 56, and thus the image-forming substrate 54' cannot be utilized to produce a transparency film for the overhead projector. Nevertheless, the image-forming substrate 541 is useful and advantageous in view of another aspect.

In particular, when a monochromatic dye or ink is encapsulated in a microcapsule as in the case of the first embodiment, a shell of the microcapsule cannot be transparent. Namely, the microcapsule shell must be colored with the same single color pigment as the color (usually, white) of the sheet of paper 561. In this case, when the microcapsule is compacted and broken so that a single color is exhibited due to a seepage of the monochromatic dye or ink from the compacted and broken microcapsule, the exhibited single color may be influenced by the single color pigment of the shell of the compacted and broken microcapsule because the shell of the compacted and broken microcapsule cannot necessarily be

completely hidden by the seeped monochromatic dye or ink, as shown by way of example in Fig. 5. For example, when the single color pigment of the microcapsule shell is white, the exhibited single color is thinned.

However, in the modified embodiment shown in Fig. 16, where a liquid leuco-pigment, seeped from a compacted and broken microcapsule (64C, 64M, 64Y), reacts with the color developer to thereby produce a single color, this produced single color cannot be influenced by the transparent shell of the compacted and broken microcapsule (64C, 64M, 64Y) In the embodiments shown in Figs. 14 and 16, the transparent binder solution may contain the transparent color developer which reacts with first, second and third transparent liquid leuco-pigments to produce cyan, magenta and yellow. Also, when a sufficient amount of transparent color can be contained in the transparent binder solution, the transparent color developer layer 58 may be omitted from the image-forming substrate (54, 54').

Figure 17 shows a third embodiment of an image-forming substrate of the present invention generally indicated by reference 66. Similar to the first embodiment, the image- forming substrate 66 is produced in the form of paper sheet. Namely, the image-forming substrate 66 comprises a sheet of paper 68, a white-coat 'Layer 70 formed on a surface of the paper sheet 68, a layer of microcapsules 72 coated over a surface of the white-coat layer 70, a sheet of transparent

ultraviolet barrier film 74 covering the microcapsule layer 72, and a sheet of transparent protective film 76 applied to the transparent ultraviolet barrier film 74.

The white-coat layer 70 is composed of a suitable white- pigment, and gives a desired white quality to the surface of the paper sheet 68. The microcapsule layer 72 may be identical to the microcapsule layer 14 of the first embodiment shown in Fig. 1. Namely, the cyan, magenta and yellow microcapsules, included in the microcapsule layer 72, exhibit the temperature/pressure characteristics as shown in Fig. 3. Accordingly, by suitably selecting a heating temperature and a breaking pressure which should be exerted on the image-forming substrate 66, the cyan, magenta and yellow microcapsules can be selectively compacted and broken. Thus, a color image can be formed on the image-forming substrate 66, for example by the thermal color printer shown in Fig. 6.

In the third embodiment, it is also possible to considerably improve the preservation of the color image formed on the image-forming substrate 66 due to the existence of the ultraviolet barrier film sheet 74. Namely, with the ultraviolet barrier film sheet 74, the formed color image can be prevented from deteriorating due to ultraviolet light. While the color image is formed on the image-forming substrate 66 by the thermal printer shown in Fig. 6, the ultraviolet barrier film sheet 74 may be thermally fused or melted by the thermal heads (30C, 30M and 30Y). Nevertheless, due to the

existence of the protective film sheet 76, the thermally fused ultraviolet barrier film sheet 74 is prevented from sticking to the thermal heads.

Further, in the third embodiment, the image-forming substrate 66 features an electrically conductive layer 78 formed on the other surface or back surface of the paper sheet 68. The electrically conductive layer 78 may be composed of a suitable electrically conductive coating material. In general, an image-forming substrate is susceptible to an electrical charge due to triboelectrification, and the electrically charged image-forming substrate may be entangled with the platen (32C, 32M, 32Y) due to the generation of an electrostatic attractive force between the platen and the charged image-forming substrate during a formation of the color image by the printer shown in Fig. 6. Nevertheless, with the third embodiment, the electrostatic entanglement of the image-forming substrate 66 by the platen can be prevented due to the existence of the electrical conductive layer 78.

In particular, although the image-forming substrate 66 is electrostatically charged, the electrostatic charge can be easily dissipated from the image-forming substrate 66 through the electrical conductive layer 78 during the formation of the color image by the printer because the electrical conductive layer #8 can be in electrical contact with a conductive part of the printer.

In the third embodiment, a leuco-pigment may be utilized.

In this case, a color developer, which reacts with the leuco- pigment, may be contained in the binder solution, which is used for the formation of the microcapsule layer 72. Optionally, the color developer may be contained in the white- coat layer 70.

Figure 18 shows a fourth embodiment of an image-forming substrate of the present invention generally indicated by reference 80. In this fourth embodiment, the image-forming substrate 80 is produced in the form of a seal or label sheet, a piece of which may be utilized as a seal adapted to be adhered to a post card, an envelop, a package or the like. Namely, the image-forming substrate 80 comprises a sheet of paper 82, a layer of microcapsules 84 coated over a surface of the paper sheet 82, a sheet of transparent protective film 86 covering the microcapsule layer 84, a layer of adhesive 88 formed on the other surface of the paper sheet 82, and a sheet of release paper 90 applied to the adhesive layer 88.

The microcapsule layer 84 may be identical to the microcapsule layer 14 of the first embodiment shown in Fig. 1. Namely, the cyan, magenta and yellow microcapsules, included in the microcapsule layer 84, exhibit the temperature/pressure characteristics as shown in Fig. 3. Accordingly, by suitably selecting a heating temperature and a breaking pressure, which should be exerted on the image-forming substrate 80, the cyan, magenta and yellow microcap3ules can be selectively compacted and broken. Thus, a color image can be formed on the image-

forming substrate 80, for example by the thermal color printer shown in Fig. 6.

Preferably, the image-forming substrate 80 is provided with crosswise perforated lines (not shown) so as to enable division into a plurality of rectangular sections, and respective identical or different images are formed on the rectangular sections of the image-forming substrate 80. Thereafter, one of the rectangular sections is cut off from the image-forming substrate 80, and a piece of the release paper sheet 90 is peeled therefrom whereby the rectangular section concerned can be adhered to a post card, an envelop, a package, or the like.

Similar to the third embodiment, in the fourth embodiment, a leuco-pigment may be utilized as the ink to be encapsulated in the microcapsules. In this case, a color developer, which reacts with the leuco-pigment, may be contained in the binder solution which is used for the formation of the microcapsule layer 84. optionally, a layer of color developer may be interposed between the paper sheet 82 and the microcapsule layer 84.

Figure 19 shows a fifth embodiment of an image-forming substrate of the present invention generally indicated by reference 92. In this fifth embodiment, the image-forming substrate 92 is produced in the form of a transfer film sheet.

Namely, the image-forming substrate 92 comprises a sheet of film 94 composed of a suitable synthetic resin, such as

polyethylene terephthalate, a peeling layer 96 composed of a teflon-based coating material or a silicone-based coating material and formed over a surface of the film sheet 94, a layer of a transparent ultraviolet barrier 98 formed on the peeling layer 96, and a layer of microcapsules 100 coated over the ultraviolet barrier layer 98.

The microcapsule layer 100 may be identical to the microcapsule layer 14 of the first embodiment shown in Fig. 1. Namely, the cyan, magenta and yellow microcapsules, included in the microcapsule layer 100, have the temperature/pressure characteristics, as shown in Fig. 3. Accordingly, by suitably selecting a heating temperature and a breaking pressure, which should be exerted on the image-forming substrate 92, the cyan, magenta and yellow microcapsules can be selectively compacted and broken. Thus, a color image can be formed on the image- forming substrate 92, for example by the thermal color printer shown in Fig. 6.

Further, the image-forming substrate 92 may optionally comprise an electrically conductive layer 102 formed on the other surface or back surface of the film sheet 94, and a sheet of protective film 104 is applied to the electrical conductive layer 102.

As shown in Fig. 20, the image-forming substrate 92 is used together with a printing sheet of paper P. Namely, the image-forming substrate 92, overlaid with the printing paper sheet P, is fed in the printer shown in Fig. 6 such that the

protective film sheet 104 contacts the thermal heads (30C, 30M and 30Y), and the cyan, magenta and yellow microcapsules are selectively compacted and broken in accordance with respective digital color image-pixel signals. Thus, as conceptually shown in Fig. 20, ink, seeped from the compacted and broken microcapsules, is transferred from the image-forming substrate 92 to the printing paper sheet P,. Namely, a color image is formed on the image-forming substrate 92, and the formed color image is transferred to the printing paper sheet P.

When the image-forming substrate 92 is heated by the thermal heads (30C, 30M and 30Y), the transparent ultraviolet barrier layer 98 is thermally fused or melted locally in accordance with the digital color image-pixel signal. Thus, as shown in Fig. 20, the ink, transferred from the image- forming substrate 92 to the printing sheet paper P, is covered with a thermaily-fused transparent ultraviolet barrier material 98' derived from the transparent ultraviolet barrier layer 98. Accordingly, it is possible to considerably improve the preservation of a transferred color image formed on the printing paper sheet P due to the existence of the thermally- fused transparent ultraviolet barrier material 98'.

Similar to the third embodiment, in the fifth embodiment, during the formation of a color image on the printing sheet paper P by the printer shown in Fig. 6, an electrostatic entanglement of the image-forming substrate 92 with the platen can be prevented due to the existence of the electrically

conductive layer 102. Namely, during the formation of the color image by the printer, the back surface of the image- forming substrate 92 is in contact with a grounded conductive element of the printer (not shown in Fig. 6), whereby an electrostatic charge can be easily dissipated from the image- forming substrate 92 through the electrically conductive layer 102. Also, during the formation of the color image by the printer, although the electrically conductive layer 102 may be thermally fused or melted by the thermal heads (30C, 30M, 30Y), the thermally-fused electrical conductive layer 102 is prevented from sticking to the thermal heads due to the existence of the protective film sheet 104.

In the fifth embodiment, optionally, a leuco-pigment may be utilized as the ink to be encapsulated in the microcapsules. In this case, as shown in Fig. 21, a layer of color developer 106 is formed over the paper sheet P.

Figure 22 shows a sixth embodiment of an image-forming substrate of the present invention generally indicated by reference 108. In this sixth embodiment, the image-forming substrate 108 is also produced in the form of a transfer film sheet. Namely, the image-forming substrate 108 comprises a sheet of transparent film 110 composed of a suitable synthetic resin, such as polyethylene terephthalate, a transparent peeling layer 112 composed of a teflon-based coating material or a silicone-based coating material and formed over a surface of the film sheet 110, a layer of transparent ultraviolet

barrier 114, and a layer of microcapsules 116 coated over the ultraviolet barrier layer 114.

The microcapsule layer 116 may be identical to the microcapsule layer 14 of the first embodiment shown in Fig. 1, except that the shell of the cyan, magenta and yellow microcapsules is formed of a transparent shape memory resin. Namely, the cyan, magenta and yellow microcapsules included in the microcapsule layer 114 have the temperature/pressure characteristics as shown in Fig. 3. Accordingly, by suitably selecting a heating temperature and a breaking pressure, which should be exerted on the image-forming substrate 108, the cyan, magenta and yellow microcapsules can be selectively compacted and broken. Thus, a color image can be formed on the image-forming substrate 108, for example by the thermal color printer shown in Fig. 6.

As shown in Fig. 23, the image-forming substrate 108 is used together with a printing sheet of paper P. Namely, the image-forming substrate 108, overlaid with the printing paper sheet P, is fed in the printer shown in Fig. 6 such that the printing paper sheet P contacts the thermal heads (30C, 30M and 30Y), and the cyan, magenta and yellow microcapsules are selectively compacted and broken in accordance with respective digital color image-pixel signals. Thus, as conceptually shown in Fig. 23, ink discharged from the compacted and broken microcapsules is transferred from the image-forming substrate 108 to the printing paper sheet P. Namely, a color image is

formed on the image-forming substrate 108, and the formed color image is transferred to the printing paper sheet P. Similar to the fifth embodiment, in this six embodiment, when the image-forming substrate 108 is heated by the thermal heads (30C, 30M, 30Y), the transparent ultraviolet barrier layer 114 is thermally fused or melted locally in accordance with the digital color image-pixel signal. Thus, as shown in Fig. 23, the ink transferred from the image-forming substrate 108 to the printing sheet paper P is covered with a thermally- fused transparent ultraviolet barrier material 1141 derived from the transparent ultraviolet barrier layer 114. Accordingly, it is possible to considerably improve the preservation of a transferred color image formed on the printing paper sheet P due to the existence of the thermally- fused transparent ultraviolet barrier material 114'.

With the sixth embodiment, after a frame of color image is completely transferred to the printing paper sheet P, the remaining image-forming substrate 108 can be utilized as a transparency film carrying a negative frame of the color image due to the transparent film sheet 110 and the transparent shells of the cyan, magenta and yellow microcapsules being included in the microcapsule layer 116.

In the sixth embodiment, a transparent leuco-pigment may be utilized as an ink to be encapsulated in the microcapsules. In this case, as shown in Fig. 24, a layer of color developer 118 is formed over the paper sheet P. Of course, in the

embodiment of Fig. 24, after a frame of a color image is completely transferred to the printing paper sheet P, the remaining image-forming substrate 108 cannot be utilized as a transparency film carrying a negative frame of the color image because the leuco-pigments encapsulated in the microcapsules are transparent. Nevertheless, the remaining transparent image-forming sheet 108 can be recycled for a certain purpose due to the transparency characteristic thereof. For example, the remaining transparent image-forming substrate 108 can be used as a wrapping sheet.

Figure 25 shows a seventh embodiment of an image-forming substrate of the present invention generally indicated by reference 120. In this seventh embodiment, the image-forming substrate 120 is produced in the form of a board paper sheet, which may be advantageously utilized as a post card. Namely, the image-forming substrate 120 comprises a sheet of board paper 122, a layer of microcapsules 124 coated over a surface of the board paper sheet 122, and a sheet of transparent protective film 126 covering the microcapsule layer 124.

The microcapsule layer 124 may be identical to the microcapsule layer 14 of the first embodiment shown in Fig. 1. Namely, the cyan, magenta and yellow microcapsules, included in the microcapsule layer 124 have the temperature/pressure characteristics as shown in Fig. 3. Accordingly, by suitably selecting a heating temperature and a breaking pressure, which should be exerted on the image-forming substrate 120, the

cyan, magenta and yellow microcapsules can be selectively compacted and broken. Thus, a color image can be formed on the image-forming substrate 120, for example by the thermal color printer shown in Fig. 6.

Note, the spring-biasing units (34C, 34M and 34Y) are of course adjustable in accordance with the thickness of the image-forming substrate 120 such that the platens (32C, 32M, 32Y) can be elastically pressed against the thermal heads (30C, 30M, 30Y) at the required predetermined pressures.

In the seventh embodiment, the image-forming substrate 120 features a heat-sensitive recording layer 128 formed on the other surface of the board paper sheet 122. The heat- sensitive recording layer 128 per se is well known. Namely, the heat-sensitive recording layer 128, which usually exhibits a white surface, is changed into a black surface when the heat-sensitive recording layer 128 is heated to beyond a predetermined temperature.

Accordingly, when the image-forming substrate 120 is fed in the printer shown in Fig. 6 such that the transparent protective film contacts the thermal heads (30C, 30M and 30Y), the cyan, magenta and yellow microcapsules are selectively compacted and broken in accordance with respective digital color image-pixel signals whereby a color image is formed on the microcapsule layer 124 of the image-forming substrate 120.

On the other hand, by actuating one of the thermal heads (30C, 30M and 30Y) of the printer, black images, such as black

characters, can be formed and recorded on the heat-sensitive recording layer 128 of the image-forming substrate 120. Of course, in this case, the image-forming substrate 120 is fed in the printer such that the heat-sensitive recording layer 128 contacts the thermal heads (30C, 30M and 30Y).

Note, during the formation of the color image on the microcapsule layer 124 of the image-forming substrate 120 by the thermal heads (30C, 30M and 30Y), the heat-sensitive recording layer 128 cannot be thermally influenced by the thermal heads, due to the sufficient thickness of the board paper sheet 122. of course, the same is true for the microcapsule layer 124 when forming an image on the heat- sensitive recording layer 128.

Similar to the fourth embodiment, in the seventh embodiment, a leuco-pigment may be utilized as the ink to be encapsulated in the microcapsules. In this case, a color developer, which reacts with the leuco-pigment, is be contained in the binder solution which is used for the formation of the microcapsuie layer 124. Optionally, a layer of color developer may be interposed between the board paper sheet 122 and the microcapsule layer 124.

Figure 26 shows an eighth embodiment of an image-forming substrate of the present invention generally indicated by reference 130. In this eighth embodiment, the image-forming substrate 130 is produced in a form of a paper sheet. Namely, the image-forming substrate 130 comprises a sheet of suitable

transparent resin 132, a layer of microcapsules 134 coated over a surface of the transparent resin sheet 132, and a sheet of transparent protective film 136 covering the microcapsule layer 134.

The microcapsule layer 134 may be identical to the microcapsule layer 14 of the first embodiment shown in Fig. 1. Namely, the cyan, magenta and yellow microcapsules, included in the microcapsule layer 134, have the temperature/pressure characteristics as shown in Fig. 3. Accordingly, by suitably selecting a heating temperature and a breaking pressure, which should be exerted on the image-forming substrate 130, the cyan, magenta and yellow microcapsules can be selectively compacted and broken. Thus, a color image can be formed on the image-forming substrate 130, for example by the thermal color printer shown in Fig. 6.

In the eighth embodiment, the image- forming substrate 130 also features a heat-sensitive recording layer 138 formed on the other surface of the transparent resin sheet 132. The heat-sensitive recording layer 138 is identical to the heat- sensitive recording layer 128 of the seventh embodiment. Namely, the heat-sensitive recording layer 138 usually exhibits a white surface, but the white surface is changed into a black surface when the heat-sensitive recording layer 138 is heated to beyond a predetermined temperature, as indicated by the reference TUL of Fig. 3.

As is apparent from the description accompanying Fig. 13,

a dot area, in which a black dot should be produced on the microcapsule layer 134, is successively heated by three resistance elements (Rcn, Rmn and Ryn) of the thermal heads (30C, 30M, 30Y), which correspond to each other. Thus, the temperature of the above-mentioned dot area exceeds the predetermined temperature (TUL) due to the successive heating by the three resistance elements (Rcnf Rmn and Ryn) - Accordingly, a white area of the heat-sensitive recording layer 138, corresponding to the black dot produced on the microcapsule layer 134 is thermally changed into a black area.

As is well known, it is possible to produce black by mixing the three primary-colors: cyan, magenta and yellow, but, in reality, it is difficult to generate a true or vivid black by the mixing of the primary colors. Nevertheless, with the eighth embodiment, it is possible to easily obtain a suitable black due to the existence of the heat-sensitive recording layer 138.

Similar to the fourth embodiment, in the eighth embodiment, a leuco-pigment may be utilized as the ink to be encapsulated in the microcapsules. In this case, a transparent color developer, which reacts with the leuco- pigment, is contained in the binder solution which is used for the formation of the microcapsule layer 134. Optionally, a layer of transparent color developer may be interposed between the transparent resin sheet 132 and the microcapsule layer 134.

Figure 27 shows a ninth embodiment of an image-forming substrate of the present invention generally indicated by reference 140. In this ninth embodiment, the image-forming substrate 140 is produced in a form of a duplicating-paper sheet or a double-recording-paper sheet. Namely, the image- forming substrate 140 comprises a first image-forming substrate element 142, a second image-forming substrate element 144, and a peeling layer 146, interposed between the first and second image-forming substrate elements 142 and 144, which is composed of a teflon-based coating material or a silicone-based coating material.

In particular, the first image-forming substrate element 142 includes a first sheet of paper 142A, a first layer of microcapsules 142B coated over a surface of the first paper sheet 142A, and a sheet of transparent protective film 142C covering the first microcapsule layer 142B. The second image forming substrate element 144 includes a second sheet of paper 144A and a second layer of microcapsules 144B coated over a surface of the second paper sheet 144A. The peeling layer 146 is provided between the other surface of the first paper sheet 142A and the second microcapsule layer 144B, as shown in Fig. 29, and is formed on and adhered to the other surface of the first paper sheet 142A with a larger adhesive force than that between the second microcapsule layer 144B and the peeling layer 146. Namely, the second image-forming substrate element 144 can be easily peeled from the peeling layer 146 when the

image-forming substrate 140 is separated into the two substrate elements 142 and 144.

In the ninth embodiment, the first microcapsule layer 142B is substantially identical to the microcapsule layer 14 of the first embodiment shown in Fig. 1. Namely, the cyan, magenta and yellow microcapsules included in the first microcapsule layer 142B exhibit the temperature/pressure characteristics as shown in Fig. 3. Accordingly, by suitably selecting a heating temperature and a breaking pressure, which should be exerted on the first image-forming substrate element 142, the cyan, magenta and yellow microcapsules can be selectively compacted and broken. Thus, a color image can be formed on the first image-forming substrate element 142.

Similar to the microcapsule layer 14 of the first embodiment shown in Fig. 1, the second microcapsule layer 144B is formed from three types of microcapsules: a first type of microcapsules is filled with cyan liquid dye or ink, a second type of microcapsules is filled with magenta liquid dye or ink, and a third type of microcapsules is filled with yellow liquid dye or ink. These three types of microcapsules are uniformly distributed in the second microcapsule layer 144B. The respective cyan, magenta and yellow microcapsules included in the second microcapsule layer 144B exhibit temperature/pressure characteristics indicated by a solid line, a single-chained line and a double-chained line in Fig. 28. Accordingly, by suitably selecting a heating temperature

and a breaking pressure, which should be exerted on the second image-forming substrate element 144, the cyan, magenta and yellow microcapsules can be selectively compacted and broken. Thus, a color image can be formed on the second image-forming substrate element 144.

As is apparent from the a graph of Fig. 28, the shape memory resin of the cyan microcapsules is prepared so as to exhibit a characteristic longitudinal elasticity coefficient having a glass-transition temperature T1', indicated by the solid line; the shape memory resin of the magenta microcapsules is prepared so as to exhibit a characteristic longitudinal elasticity coefficient having a glass-transition temperature T2', indicated by the single-chained line; and the shape memory resin of the yellow microcapsules is prepared so as to exhibit a characteristic longitudinal elasticity coefficient having a giass-transition temperature T31, indicated by the double-chained line. Also, the glass- transition temperatures T1', T2' and T3' are lower than the glass-transition temperatures T1, T2 and T3, shown in the graph of Fig. 3.

Accordingly, when the image-forming substrate 140 is fed in the printer shown in Fig. 6 such that the transparent protective film 142C contacts the thermal heads (30C, 30M and 30Y), the cyan, magenta and yellow microcapsules included in the first microcapsule layer 142B, and the cyan, magenta and yellow microcapsules, included in the second microcapsule

layer 144B, are selectively compacted and broken in accordance with respective digital color image-pixel signals whereby two color images can be simultaneously formed on the first and second microcapsule layers 142B and 144B of the image-forming substrate 140.

In particular, when the image-forming substrate 140 is heated by the thermal heads (30C, 30M and 30Y), the temperature at the second microcapsule layer 144B is lower than the temperature at the first microcapsule layer 142B due to the interposition of the first paper sheet 142A and the peeling layer 146 between the first and second microcapsuie layers 142B and 144B. Nevertheless, since the glass- transition temperatures Ti', T2' and T3 ' shown in Fig. 28 are set to be correspondingly lower than the glass-transition temperatures T1, T2 and T3 shown Fig. 3, the simultaneous formation of the respective color images on the first and second microcapsule layers 142D and 1443 is made possible.

As already stated hereinbefore, the second image-forming substrate element 144 can be easily peeled from the peeling layer 146 when the image-forming substrate 140 is torn into the two substrate elements 142 and 144. Accordingly, after the simultaneous formation of the respective color images on the first and second microcapsule layers 142B and 144B, it is possible to individually obtain the respective first and second image-forming substrate elements 142 and 144 carrying the formed color images, as shown in Fig. 29.

Similar to the fourth embodiment, in the eighth embodiment, a leuco-pigment may be utilized as the ink to be encapsulated in the microcapsules. In this case, a transparent color developer, which reacts with the leuco- pigment, is contained in the two respective binder solutions which are used for the formation of the first and second microcapsule layers 142B and 144B. Optionally, a first layer of color developer may be interposed between the first paper sheet 142A and the first microcapsule layer 142B, and a second layer of color developer may be interposed between the second paper sheet 144A and the second microcapsule layer 144B.

Figure 30 shows a tenth embodiment of an image-forming substrate of the present invention generally indicated by reference 148. Similar to the ninth embodiment, in this tenth embodiment, the image-forming substrate 148 is produced in a form of a duplicating-paper sheet or a double-recording-paper sheet. Namely, the image-forming substrate 148 comprises a first image-forming substrate element 1SO, a second image- forming substrate element 152, and a peeling layer 154, interposed between the first and second image-forming substrate elements 1SO and 152 and composed of a teflon-based coating material or a silicone-based coating material.

In particular, the first image-forming substrate element 150 includes a first sheet of paper 150A, a first layer of microcapsules 150B coated over a surface of the first paper sheet 150A, and a sheet of transparent protective film 1SOC

covering the first microcapsule layer 150B. The second image forming substrate element 152 includes a second sheet of paper lS2A, a layer of color developer 152B formed over the second paper sheet 152A, and a second layer of microcapsules 152C coated over the color developer layer 1S2B. The peeling layer 154 is provided between the other surface of the first paper sheet 150A and the second microcapsule layer 152C, as shown in Fig. 30.

In the tenth embodiment, the first microcapsule layer 150B is substantially identical to the microcapsule layer 14 of the first embodiment shown in Fig. 1. Namely, the cyan, magenta and yellow microcapsules included in the first microcapsule layer 1S2B exhibit the temperature/p-ressure characteristics as shown in Fig. 3. Accordingly, by suitably selecting a heating temperature and a breaking pressure, which should be exerted on the first image-forming substrate element 150, the cyan, magenta and yellow microcapsules can be selectively compacted and broken. Thus, a color image can be formed on the first image-forming substrate element 150.

However, the second microcapsule layer 152C is formed from three types of microcapsules: a first type of microcapsules is filled with a first liquid leuco-pigment, a second type of microcapsules is filled with a second liquid leuco-pigment, and a third type of microcapsuies is filled with a third liquid leuco-pigment. The respective first, second and third liquid leuco-pigments react with the color

developer, included in the color developer layer 1523, to thereby produce cyan, magenta and yellow. The respective first, second and third microcapsules included in the second microcapsule layer 152C exhibit the temperature/pressure characteristics as shown in the graph of Fig. 29. Thus, by suitably selecting a heating temperature and a breaking pressure, which should be exerted on the second image-forming substrate element 152, the first, second and third microcapsules can be selectively compacted and broken. Thus, a color image can be formed on the second image-forming substrate element 152.

Accordingly, similar to the ninth embodiment, when the image-forming substrate 148 is fed in the printer shown in Fig. 6 such that the transparent protective film 150C contacts the thermal heads (30C, 30M and 30Y), the cyan, magenta and yellow microcapsules, included in the first microcapsule layer 150B, and the first, second and third microcapsules, included in the second microcapsule layer 152C, are selectively compacted and broken in accordance with respective digital color image-pixel signals whereby two color images can be simultaneously formed on the first and second microcapsule layers 1SOB and 152C of the image-forming substrate 148.

In the image-forming substrate 148, the peeling layer 154 is formed on and adhered to the other surface of the first paper sheet 150A with a,sufficiently large adhesive force. Also, the microcapsule shells of the second microcapsule layer

152C are adhered to the peeling layer 154 with a larger adhesive force than that which adheres the microcapsule shells of the second microcapsule layer 152C to the color developer layer 152B. However, the leuco-pigment seeped from a compacted and broken microcapsule can be easily separated from the peeling layer 154. Accordingly, after the simultaneous formation of the respective color images on the first and second microcapsule layers 150B and 152C, when the image- forming substrate 148 is torn into the two substrate elements 150 and 152, the second paper sheet 1S2A with the color developer layer lS2B carrying the formed color image is peeled from the peeling layer 1S4, as shown in Fig. 31.

With the tenth embodiment, since the second paper sheet 152A with the color developer layer 1S2B carrying the formed color image has no unbroken microcapsules, the formed color image cannot be subjected to damage even if a large external force is exerted on the second paper sheet 152A and even if the second paper sheet IL52A is carelessly heated.

Figure 32 shows another microcapsule filled with a dye or ink for use in the present invention. In this drawing, respective references 156C, 156M and 156Y indicate a cyan microcapsule, a magenta microcapsule, and a yellow microcapsule. A shell wall of each microcapsule is formed as a double-shell wall. The inner shell wall element (158C, 1S8M, lS8Y) of the double-shell wall is formed of a shape memory resin, and the outer shell wall element (160C, 160M,

160Y) is formed of a suitable resin, which does not exhibit a shape memory characteristic.

As is apparent from the graph in Fig. 33, the inner shell walls 158C, 158M and 158Y exhibit characteristic longitudinal elasticity coefficients indicated by a solid line, a single- chained line and a double-chained line, respectively, and these inner shells are selectively broken and compacted under the temperature/pressure conditions as mentioned above.

However, the outer shell walls 160C, 160M and 160Y exhibit temperature/pressure breaking characteristics indicated by reference BPC, BPM and BPY, respectively.

Namely, the outer shell wall 160C is compacted and broken when subjected to a pressure beyond BP3; the outer shell wall 160M is compacted and broken when subjected to a pressure beyond BP2; and the outer shell wall 160Y is compacted and broken when subjected to a pressure beyond BP1. Thus, as shown in the graph of Fig. 33, a cyan-producing area, a magenta-producing area and a yellow-producing area being a hatched area C, a hatched area M and a hatched area Y, respectively, are defined by a combination of the characteristic longitudinal elasticity coefficients (indicated by the solid line, single-chained line and double-chained line) and the temperature/pressure breaking characteristics BPC, BPM and BPY.

Note, by suitably varying compositions of well-known resins and/or by selecting a suitable resin from among well-

known resins, it is possible to easily obtain microcapsules that exhibit the temperature/pressure breaking characteristics BPC, BPM and BPY.

According to the microcapsules 156C, 156M and 156Y shown in Fig. 32, regardless of the characteristic longitudinal elasticity coefficient of each microcapsule, it is a possible option to accurately determine a critical breaking pressure for each microcapsuie.

Note, in the embodiment shown in Fig. 32, the inner shell wall element (158C, 1S8M, 158Y) and the outer shell wall element (160C, 160M, 160Y) may be reversed. Namely, when the outer shell wall element of the double-shell wall is formed of the shape memory resin, and the inner shell wall element is formed of the suitable resin, which does not exhibit the shape memory characteristic.

Figure 34 shows yet another microcapsule filled with a dye or ink for use in the present invention. In this drawing, respective references 162C, 162M and 162Y indicate a cyan microcapsule, a magenta microcapsule, and a yellow microcapsule. A shell wall of each microcapsule is formed as a composite shell wall. In this embodiment, each composite shell wall comprises an inner shell wall element (164C, 164M, 164Y), an intermediate shell wall element (166C, 166M, 166Y) and an outer shell element (168C, 168M, 168Y), and these shell wall elements are formed, from suitable resins, which do not exhibit shape memory characteristics.

In the graph in Fig. 35, the inner shell walls 164C, 164M and 164Y exhibit temperature/pressure breaking characteristics indicated by references INC, INM and INY, respectively. Also, reference IOC indicates a resultant temperature/pressure breaking characteristic of both the intermediate and outer shell walls 166C and 168C; reference IOM indicates a resultant temperature/pressure breaking characteristic of both the intermediate and outer shell walls 166M and 168M; and reference IOY indicates a resultant temperature/pressure breaking characteristic of both the intermediate and outer shell walls 166Y and 168Y.

Thus, as shown in the graph of Fig. 35, by a combination of the temperature /pressure breaking characteristics (INC, INM and INY; IOC, IOM and IOY) , a cyan-producing area, a magenta- producing area and a yellow-producing area are defined as a hatched area C, a hatched area M and a hatched area Y, respectively.

Note, similar to the above-mentioned case, by suitably varying compositions of well known resins, by selecting a suitable resin from among the well-known resins, and/or by suitably regulating a thickness of each shell wall, it is possible to easily obtain resins exhibiting the temperature /pre s sure breaking characteristics (INC, INM and INY; IOC, IOM and IOY).

According to the microcapsules 162C, 162M and 162Y, shown in Fig. 34, both the critical breaking temperature and

pressure for each microcapsule can be optimally and exactly determined.

Although all of the above-mentioned embodiments are directed to the formation of a color image, the present invention may be applied to the formation of a monochromatic image. In this case, the layer of microcapsules (14, 60, 72, 84, 100, 116, 124, 134, 142B, 144B, 150B, 152C) is composed of only one type of microcapsule filled with, for example, a black ink. Also, as shown in Fig. 36, a cyan microcapsule layer, a magenta microcap5ule layer and a yellow micrccapsule layer may be formed on divided area sections C, M and Y, respectively, of a single image-forming substrate. When this image-forming substrate is fed in the printer shown in Fig. 6, a cyan image is formed on the area of section C by the thermal head (30C); a magenta image is formed on the area of section M by the thermal head (30M); and a yellow image is formed on the area of section Y by the thermal head (30Y).

Finally, it will be understood by those skilled in the art that the foregoing description is of preferred embodiments of the image-forming substrate, and that various changes and modifications may be made to the present invention without departing from the scope thereof.

Claims

Claims: 1. An image-forming substrate comprising:- a sheet of board paper; a layer of microcapsules, coated over a surface of said board paper sheet, that contains at least one type of microcapsules filled with a dye, said microcapsules exhibiting a temperature/pressure characteristic such that when respective said microcapsules are squashed under a predetermined pressure at a predetermined temperature, said liquid dye seeps from said squashed microcapsule; and a heat-sensitive recording layer formed on another surface of said board paper sheet.
2. An image-forming substrate comprising:- a transparent sheet composed of a suitable transparent synthetic resin; a layer of microcapsules, coated over a surface of said transparent sheet, that contains at least one type of microcapsules filled with a dye, said microcapsules exhibiting a temperature/pressure characteristic such that when respective said microcapsules are squashed under a predetermined pressure at a predetermined temperature, said liquid dye seeps from said squashed microcapsule; and a heat-sensitive recording layer formed on another surface of said transparent sheet.
3. An image-forming substrate substantially as herein described with reference to the accompanying drawings.