JPH0485073A - Heat sensitive transfer material - Google Patents

Abstract

PURPOSE:To provide each image dot with a different energy and control printing density so as to produce a gradient recording by incorporating in a transfer surface a plurality of kinds of thermally expandable particles, each having a different expansion starting temperature. CONSTITUTION:When the heating resistor of a thermal head 360 is energized, Joule heat is generated and transmitted through a base film 450 of an ink ribbon 400 to a thermally meltable ink layer 410. The thermally meltable ink layer 410 is then melted by this heat into a liquid ink and, at the same time, the microcapsules 420 are expanded to be increased in volume. In doing so, the molten ink on the thermally meltable ink layer 410 is released from the surface of the ink ribbon 400 and forced against an uneven surface of recording paper P to be impressed thereon. A plurality of kinds of microcapsules 420, each having a different expansion temperature, is dispersed in the thermally meltable ink layer 410 and the energy applied to a thermal head 360 is controlled, whereby the microcapsules 420 are selectively expanded to change the amount of the ink impressed on the recording paper P.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention relates to a thermal transfer material used in a thermal transfer recording type image forming apparatus.

(Prior art) In recent years, image forming devices such as printers and facsimiles using thermal transfer recording methods have become popular because they do not make noise during operation, are low in cost, easy to reduce in size and weight, and have excellent operability and maintainability. It is becoming widespread.

This thermal transfer method generally uses a thermal transfer material (hereinafter referred to as an ink ribbon) that has a heat-melting ink layer on a sheet-like support, and selectively transfers this ink ribbon using a thermal head or the like. The ink layer is heated to melt the ink layer, and the melted ink is transferred onto a recording medium to record an image according to the heated shape.

By the way, conventional ink ribbons have a problem in that print quality deteriorates on recording media with poor surface smoothness. Therefore, in order to be able to perform good printing even on recording media with poor surface smoothness, thermal expansion ink is made of a shell containing a thermal expansion substance in a heat-melting ink layer or in a separate layer. (hereinafter referred to as microcapsules).

) has been developed.

When this ink ribbon is heated by a thermal head, the ink layer melts and the microcapsules expand, and the pressure causes the molten ink to be pressed and adhered to the recording medium, resulting in a smooth surface. Good printing can be performed even on recording media with poor quality.

However, with the ink ribbon containing the above-mentioned microcapsules, it is difficult to perform V@ tone recording by controlling the print density for each pixel.

(Problems to be Solved by the Invention) As mentioned above, an ink ribbon containing microcapsules in a heat-melting ink layer can print well even on recording media with poor surface smoothness. On the other hand, there is a problem in that it is difficult to perform gradation recording by controlling the print density for each pixel.

The present invention was made to solve such problems,
- To provide a thermal transfer material capable of performing Rji tone recording by controlling the print density for each image point.

[Structure of the Invention (Means for Solving the Problems) The present invention provides a thermal transfer material provided with a transfer surface containing thermally expandable particles consisting of a shell and a thermally expandable material contained in the shell, The thermally expandable particles are composed of a plurality of substances whose shells have different softening start temperatures.

A second invention is a thermal transfer material provided with a transfer surface containing thermally expandable particles consisting of a shell and a thermally expandable material included in the shell, wherein the thermally expandable particles are It is composed of multiple substances with different values.

A third invention is a thermal transfer material provided with a transfer surface containing thermally expandable particles consisting of a shell and a thermally expandable material contained in the shell, wherein the thermally expandable particles have an inner diameter of the shell. It consists of multiple different species.

A fourth invention is a thermal transfer material provided with a transfer surface containing thermally expandable particles consisting of a shell and a thermally expandable material contained in the shell, wherein the thermally expandable particles are formed of the thermally expandable material. It consists of multiple types with different ratios of specific gravity and molecular weight.

(Function) In the first invention, the thermally expandable particles contained in the transfer surface are
There are multiple types of thermally expandable particles whose shells have different softening start temperatures. Further, in the second invention, a plurality of types of thermally expandable particles having different shell thicknesses are used. Since the strength of the shell differs depending on the thickness of the shell, the expansion start temperature of each thermally expandable particle differs.

Further, in the third aspect of the invention, a plurality of types of thermally expandable particles having different inner diameters of shells are used. Since the strength of the shell varies depending on the inner diameter of the shell, the expansion start temperature of each thermally expandable particle is different.

Furthermore, in the fourth aspect of the invention, there are a plurality of types of thermally expandable particles having different ratios between the specific gravity and the molecular weight of the thermally expandable material. Since the vaporization pressures of the thermally expandable materials at room temperature are different, the expansion start temperatures of the respective thermally expandable particles are different.

In this way, since the transfer surface contains multiple types of thermally expandable particles with different expansion start temperatures, the number of thermally expandable particles that expand depending on the temperature when heated changes, so it is difficult to extrude. The amount of ink also changes. Therefore, by changing the energy applied to each pixel, it is possible to control the print density and perform gradation recording.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

Image forming apparatus FIG. 1 shows an image forming apparatus 10 according to an embodiment of the present invention.
FIG. The configuration will be explained below.

The recording paper cassette 60 stores recording paper P.

Further, as a conveyance mechanism for this recording paper P, there is a take-out mechanism 70 that sends out the recording paper P from the cassette 60, a separation mechanism 90 that separates and conveys the recording paper P taken out from the cassette 60 one by one, and a PET (polyethylene terephthalate). ,
A drum 100, which has a dielectric material such as polyimide formed on its surface and conveys the recording paper P while adsorbing it to its surface.
a pinch roller 110 that presses the recording paper P against the drum 100, a peeling claw 130 that peels off the recording paper P from the drum 100, and a tray 15.
There is a paper discharge mechanism 140 for discharging the recording paper P on the top of the recording paper P.

Also, around the drum 100, there are a recording paper detection sensor 120 that detects the leading and trailing edges of the recording paper P, a monochrome printing mechanism 300 that prints only colors, and a color printing mechanism 600 that performs color printing. It is located.

Furthermore, the image forming apparatus 10 includes an interface for receiving image signals from the outside, an electric circuit 200 for controlling the entire apparatus, a power supply 280 for supplying power to each part of the apparatus, and a control panel 290 for performing various operations of the apparatus.
Or is provided.

Next, the operation in the above configuration will be explained. The recording paper P is transferred to the recording paper cassette 60 by the take-out mechanism 70 and the separation mechanism 90.
The sheets are taken out one by one from the pinch roller 110 and the drum 10.
Due to the suction action of 0, it is wound around the drum 100 which rotates in the direction indicated by the arrow in the figure.

Next, in the case of printing only in - color, after being printed by the monochrome printing mechanism 300, it is peeled off from the drum 100 by the peeling claw 130, and is discharged onto the tray 150 by the paper discharge mechanism 140.

On the other hand, in the case of multicolor printing, the peeling claw 130 is moved to a position away from the drum 100 indicated by the broken line by a solenoid (not shown), and the recording paper P is not printed by the monochrome printing mechanism 300 and is removed from the drum]00 The paper reaches the color printing mechanism 600 while being wound around the paper, and first, the first color is printed. Further, as the drum 100 rotates, the color printing mechanism 600 prints the second and third colors, and the monochrome printing mechanism 300 prints black, and then the peeling claw 130 moves to the position shown by the solid line to remove the recording paper P from the drum. It is peeled off from 100 and discharged onto tray 150.

The configuration and operation of each part will be explained in detail below.

Monochrome Printing Mechanism FIG. 2 is a sectional view showing the monochrome printing mechanism 300. The configuration will be explained below.

The ink ribbon 400 has one end wound around a supply roll 310, is sandwiched between a pair of supply rollers 330 and 330, is in contact with a preheater 340, and is placed between a thermal head 360 biased by a compression coil spring 350 and the drum 100. ,
and a pair of collection rollers 370 and 370, and the other end is wound onto a collection roll 380.

The supply roller pair 330, 330 is directly connected to and driven by a motor (not shown), and the collection roller pair 370, 370 and the collection roll 380 are driven via a slip clutch (not shown). The conveying speed of these ink ribbon conveying sections is the circumferential speed of the drum]00 when there is no slippage due to the slipping clutch.
The relationship is that the conveyance speed of the collection roller pair 370, 370 and the collection roller 380 > the conveyance speed of the supply roller pair 330, 330, and the ink ribbon 400 is
The structure is such that a constant tension is applied to the Further, the conveyance speed of the supply roller pair 330, 330, which defines the conveyance speed of the ink ribbon 400, is set to 0.1 to 0.9 times the circumferential speed of the drum 100, particularly 0.2 to 0.330.
It is preferable to set the range to 0.5 times.

The compression coil spring 350 biases the thermal head 360 against the drum 100 with a value smaller than the normal pressing force, and the value is set to 20 to 150 g/eel, but particularly 50 to 100 g/eel. It is preferable to set it as cm.

The preheater 340 has a resistor 34 that is longer than the width of the recording paper P.
1 is wrapped and hardened with cement 342, and the outside is further covered with a Teflon sheet 343 with low frictional resistance. The surface temperature of the preheater 340 is the same as that of the ink ribbon 400.
The temperature is controlled to be lower than the ink melting point of the ink ribbon 400 by a temperature control thermistor 344 attached to the side surface of the surface that comes into contact with the ink ribbon 400 .

Note that 367 is a drive circuit mounting portion where a drive circuit for the thermal head 360 is mounted.

Next, the operation of the monochrome printing mechanism 300 having the above configuration will be explained.

Until the recording paper P wound around the drum 100 reaches the thermal head 360, the monochrome printing mechanism 3
00 is stopped, and the ink ribbon 4
00 is in a state of sliding relative to the drum 100. Then, when the recording paper P reaches the thermal head 360 based on the detection signal from the recording paper detection sensor 120 and the delay timer in the electric circuit 200, the motor rotates, and the supply roller pair 330, 330 and the collection roller pair 370 are rotated.
．． 370 and the collection roll 380 are the ink ribbon 400
is conveyed at a slower speed than the drum 100. Further, based on the detection signal from the recording paper detection sensor 120 and the delay timer in the electric circuit 200, when the recording paper P has finished passing the thermal head 360, the motor is stopped and the conveyance of the ink ribbon 400 is stopped.

Conveyance of the ink ribbon 400 is temporarily stopped under control from the electric circuit 200 for non-image areas that are not printed, such as between lines.

Immediately before reaching the thermal head 360, the ink ribbon 400 is heated by a preheater 340 to a temperature slightly lower than the melting point of the ink, and then printed on the recording paper P by the thermal head 360. Therefore, a good transferred image can be obtained even with less heating by the thermal head 360, and high-speed recording is also possible.

Ink Ribbon FIG. 3 is a sectional view showing the structure of the ink ribbon 400. Ink ribbon FIG.

As shown in the figure, the ink ribbon 400 is composed of a heat-melting ink layer 410 that softens and melts when heated, microcapsules 420 that rapidly expands when heated, and a hese film 450 as a support for these. Microcapsules 420 are dispersed in contact with base film 450.

As for the form of dispersion, the heat-fusible ink layer 410 may be thicker than the particle size of the microcapsules 420, as shown in FIG. 3(a); The thickness of the layer 410 may be the same (FIG. 4(b)), or the heat-melting ink layer 410 may be made thinner than the particle size of the microcapsules 420.
The microcapsules 420 may be made to cover the heat-melting ink layer 410 (FIG. 2(C)), or the microcapsules 420 may be exposed from the heat-melting ink layer 410 (FIG. 4(D)).

The particle size of the microcapsules 420 is 1 to 30μ before expansion.
m, (1 to IOμm), maximum particle size after expansion is 2 to 10
0 μm1 (10 to 60 μm), heat-melting ink layer 410
The thickness is set to 1 to 20 μm1 (2 to 10 μm), and it is particularly preferable to set it to the value shown in parentheses. In addition, the amount of dispersion is 1 to 3 parts of the microcapsules 420 when the entire heat-melting ink layer 410 is 100 parts.
Preferably, it is dispersed in 0 parts.

The heat-melting ink layer 410 consists of a colorant and a binder. Examples of colorants include pigments such as carbon black,
Other examples include substances disclosed in JP-A-60-25792, such as nigrosine dye, lamp black, or any colorant commonly used in the field of printing and copying, such as various dyes, and known dyes. , all pigments can be used. In addition, as a binder, for example, JP-A-59-20
Materials disclosed in Japanese Patent No. 1894 (in parentheses below), such as waxes such as carnauba wax, paraffin, Sasol wax, and microcrystalline wax, can be used.

(Carnauba wax paraffin, Sasol wax,
Waxes such as microcrystalline wax and castor wax, stearic acid.

Higher fatty acids such as palmitic acid, lauric acid, aluminum stearate, lead stearate, barium stearate, zinc stearate, zinc palmitate methyl hydroxystearate, glycerol monohydroxystearate, or derivatives such as their metal salts and esters, polyethylene polypropylene , polyisobutylene.

Polyethylene wax, polyethylene oxide, polytetrafluoroethylene, ethylene-acrylic acid copolymer, ethylene-ethyl acrylate copolymer.

Thermoplastic resins made of olefins alone or copolymers, such as ethylene-vinyl acetate copolymers, or derivatives thereof, are used. ) Other examples (including specific examples) include beeswax, candelilla wax, polyethylene wax, hollow wax, auriculie wax, ester wax,
Oxidized wax, waxes such as monocun wax, osikelite, selenium, higher alcohols such as palmityl alcohol, stearyl alcohol, behenyl alcohol, eicosatru, higher fatty acid esters such as cetyl palmitate, myricyl palmitate, cetyl stearate, myricyl stearate, acetamide. , amides of propionic acid amide, palmitic acid amide, stearic acid amide, cellulose resins (ethyl cellulose, etc.), terpene resins, polyester resins, rosin resins, epoxy resins, vinyl resins (vinyl acetate resin, vinyl chloride) resin, vinyl chloride/vinyl acetate copolymer resin, vinyl butyral resin, polyvinyl stearate, etc.), butadiene resin, aromatic petroleum resin, low molecular weight petroleum resin, ketone resin, styrene resin, aliphatic hydrogen carbonate resin, Polyamide resin, polystyrene resin, ester resin, acrylic resin, sulfone resin, polyethylene glycol, polyacrylamide, polyvinylpyrrolidone, ester gum, rosin maleic acid resin, rosin phenolic resin, phenolic resin, terpene resin, cyclopetane diene resin, aromatic based resin,
Resins such as urea resin and silicone resin, higher amines such as stearylamine, styrene-butadiene copolymer,
Examples include high molecular weight polymers such as acetate butyrate, polyvinyl alcohol, and the like. These binders may be used alone or in combination of two or more.

As the base film 450, for example, a plastic film such as polyethylene terephthalate, polyimide, polyester, polycarbonate, triacetyl cellulose, nylon, or cellophane, or thin paper such as capacitor paper, glassine paper, or parchment paper can be used. Its thickness is 2
15 μm, particularly preferably 3 to 6 μm.

Furthermore, the base film 450 may be provided with a heat-resistant layer made of silicone resin, fluororesin, polyimide resin, epoxy resin, phenol resin, melanin resin, polyester resin, vinyl ester resin, nitrocellulose, etc. on the surface that contacts the thermal head 360, for example. It is possible to improve the 450 heat resistance of the base film.

The ink ribbon 400 in this embodiment is obtained by, for example, a known hot melt coating method or a Zurgento coating method. In the hot-melt coating method, the coating liquid mainly composed of the above-mentioned binder and colorant obtained under heating is heated to a temperature below the expansion start temperature so that the microcapsules 420 encapsulating the thermally expandable substance 430 do not expand thermally.
Disperse the microcapsules 420 in the heat-melting ink layer 410 to form a coating liquid containing the microcapsules 420 and forming the heat-melting ink layer 410 and the coating layer 470 (mainly containing the binder) at a temperature and condition below the expansion start temperature. It can be obtained by coating this using a bar coater or the like and drying it in this order.

In the solvent coating method, microcapsules 420 encapsulating the thermally expandable substance 430 are dispersed in a paint liquid containing a binder and a colorant dissolved in a solvent as main components, and the microcapsules 420 encapsulating the thermally expandable substance 430 are contained. It is obtained by preparing a coating liquid that becomes the heat-melting ink layer 410, applying it using a bar coater or the like in the same order as in the hot-melt coating method, and drying it.

Further, in the above-described ink ribbon 400, only the case where the heat-melting ink layer 410 formed on the base film 450 is one layer has been described, but a multi-layer (two or more layers) structure may be formed as necessary. You can also do that.

Next, the microcapsule 420 will be explained in more detail.

Thermal expansion material 430 encapsulated in microcapsules 420
A thermally decomposable blowing agent or a volatile liquid with a low boiling point is used.As a blowing agent, a blowing agent compound that generates gas by thermal decomposition, which is commonly used in fields such as resin processing, is used. It can also be used in the present invention. Further, as the volatile liquid, an evaporative/volatile blowing agent compound commonly used in fields such as resin processing can be used.

Thermally decomposable blowing agents include organic blowing agents such as diazoamino derivatives, azo compounds, sulfone hydrazide compounds, and nitroso compounds, and inorganic blowing agents such as bicarbonates, carbonates, and azides. Specific examples of organic blowing agents include diazoamino derivatives such as 113°bis-0-biphenylyltriazine, diazoaminobenzene, and 1-methyl-3-phenyltriazine, and azo compounds such as azobishexahydrobenzodinitrile and azo Sulfone hydrazide compounds such as dicarbonamide, azobisisobutylnitrile, diazoaminobenzene, diazoic acid amide, etc. include benzenesulfonic acid hydrazide, 4,4'bis(hydrazinosulfonyl)diphenyl ether, p-toluenesulfonylhydranthate, and henzenesulfonyl. hydrazide, p,p-oxybisbenzenesulfonylhydrazide, diphenylsulfone SS''disulfonylhydrazide, 4,4-oxydosbenzenesulfonylhydrazide, etc.Nitroso compounds include N,N--dinitroso-N,N''- Examples include dimethyl terephthalamide, N,N--dinitrosopentaethylenetetramine, N,N dimethyl-N,N--dinitroterephthalamide, and the like.

Specific examples of inorganic blowing agents include bicarbonates such as sodium bicarbonate, sodium bicarbonate, ammonium bicarbonate, and sodium bicarbonate; carbonates such as sodium bicarbonate, ammonium carbonate, and magnesium carbonate; and azides such as CaN6, Examples include BaN6. Examples of volatile liquids with low boiling points include isobutane;
Substances disclosed in the above publication, such as propane, pentane, hexane, etc., can be used. Other specific examples include trichlorofluoromethane, dichlorofluoromethane, dichlorotetrafluoroethane, n-butane, butylene,
Examples include carbon dioxide gas, acetone, methylene chloride, trichlorofluoromethane, trichlorotrifluoromethane, petroleum ether, and the like. These blowing agents may be used 1N or in combination of two or more.

In general, a low boiling point volatile liquid is a liquid at room temperature and around normal pressure. Preferred are gaseous substances that become liquid under pressure equal to or higher than normal pressure (for example, inside a microcapsule), such as isobutane, neopentane, propane, freons, and the like.

Further, the microcapsules 420 containing a foaming agent can be obtained by a known microencapsulation method. For example, in the case of an aqueous solution type, there is a spray drying method in which a non-aqueous foaming agent is dispersed in the form of a suspension or emulsion in an aqueous solution that becomes a shell material, and the resulting dispersion is spray-dried, a phase separation method, a ponbrex core, etc. Examples include cervation method, interfacial polymerization method, and in 5 situ polymerization method.

Microcapsule 420 containing a low boiling point volatile liquid
There are two types: one is a low boiling point volatile liquid itself, and the other is one in which resin particles are impregnated with a low boiling point volatile liquid. When a low boiling point volatile liquid itself is encapsulated, it can be obtained by a known microencapsulation method. For example, in the case of an aqueous solution type,
The spray drying method involves spray drying a dispersion obtained by dispersing a low-boiling point volatile liquid (insoluble in water) in the form of a suspension or emulsion into an aqueous solution that serves as a shell substance.Other methods include the phase separation method and the Pombrex core cell. Examples include vation method, interfacial polymerization method, etc.
This is disclosed in detail in Publication No. 24, etc.

Further, as the monomer that becomes the shell 440 of the microcapsules 420 obtained by polymerization, for example,
Substances disclosed in Publication No. 26524, such as styrene, 0-methylstyrene, m-methylstyrene, p-methylstyrene, ethylstyrene, ar-vinylxylene,
Alkenyl aromatics such as ar-chlorostyrene and ar-bromostyrene, styrene-derived compounds such as vinylbenzyl chloride and p-sec-butylstyrene, methyl methacrylate, ethyl acrylate, propyl acrylate, butyl acrylate, butyl methacrylate, propyl methacrylate, Acrylate substances such as butyl methacrylate, lauryl acrylate, 2-ethylhexyl acrylate, ethyl methacrylate, esters such as vinyl acetate, vinyl butyrate, vinyl acetate, vinyl laurate, vinyl myrilate, vinyl propionate, and other chlorides Examples include vinyl, vinylidene chloride, vinyl bromide, acrylonitrile, and the like.

In addition, as specific materials for the shell formed, the following substances can be mentioned in the phase separation method, interfacial polymerization method, and in 5 in situ polymerization method.

Phase separation method: polyvinyl acetate, styrene-maleic acid copolymer, benzyl cellulose, ethyl cellulose, polyethylene, nitrocellulose, ketone resin, polymethyl methacrylate, polyamide resin, acrylonitrile-styrene copolymer, vinylidene chloride-acrylonitrile copolymer, Epoxy resin, etc. Bombrex coacervation method: Gelatin, acrylic resin One-interfacial polymerization method: Polyamide, polysulfonamide, polyurea, polyurethane, polyester, polyamide urethane, polyamide urea, polysulfonamide urea, polyester sulfonate, etc. In 5 ltu polymerization method: When impregnating fine particles of resin such as polystyrene, polyurethane, urea-formalin, etc., a volatile liquid may be added during the suspension polymerization of a suitable 7-mer, for example.
Japanese Patent Publication No. 33-3190), a method in which beads obtained by suspension polymerization are swollen with a solvent etc. and a volatile liquid is added (
Japanese Patent Publication No. 36-10628), etc. Alternatively, if necessary, there is a method in which the resin is made fine and then impregnated with a volatile liquid.

Furthermore, a foaming aid may be added to adjust the decomposition temperature of the foaming agent, if necessary.

For example, compounds having the effect of lowering the decomposition temperature and substances disclosed in JP-A-60-25792, such as oxalic acid, lactic acid, and citric acid, may be mentioned. Furthermore, if necessary, it may contain a dispersant to facilitate dispersion, etc.
Surface treatment such as coating with a coloring agent can be performed. Similarly, a dispersant and a filler can be contained in the binder as necessary.

Next, the structure of microcapsules will be explained in more detail.

FIG. 4 is a perspective view showing the structure of the microcapsule 420.
/2 shows the state cut into rounds.

The microcapsule 420 is composed of a thermally expandable material 430 and a hollow shell 440 that encloses the thermally expandable material 430. Examples of the thermal expansion material 430 include a thermally decomposable blowing agent or a low boiling point volatile liquid.

It is desirable that the expansion start temperature of the microcapsules 420 containing the thermally expandable material 430 is set higher than the softening temperature of the binder. In particular, the temperature difference from the softening temperature of the binder is preferably in the range of 0°C to 50°C, and the softening temperature of the binder of the hot-melt ink layer 410 is usually 55°C to 15°C.
Since it is set to 0°C, for example, the expansion start temperature of the microcapsules 420 is preferably 55°C to 105°C when the softening temperature of the binder is 55°C, and 150°C to 200°C when the softening temperature of the binder is 150°C. The setting range is

The softening temperature of the heat-melting ink layer 410 is usually 55°C to 15°C.
Since the temperature is set at 0°C, the expansion start temperature of the microcapsules 420 containing the thermally expandable material 430 is preferably set at 80°C to 160°C, which is higher than the softening temperature of the binder.

For example, if the softening temperature of the shell 440 is higher than the thermal decomposition temperature of the blowing agent of the thermally expandable material 430 or the boiling point of the volatile liquid, the strength of the shell 440 will overcome the internal pressure even if it is heated to the softening temperature of the shell 440. No expansion occurs. That is, the expansion of the microcapsules 420 does not depend on the thermal decomposition temperature of the blowing agent of the thermally expandable material 430 or the boiling point of the volatile liquid, but rather on the softening temperature (strength) of the shell 440. Therefore, in this case shell 440
The expansion start temperature of the microcapsules 420 can be set by the material, composition, etc. of the microcapsules 420.

On the other hand, if the softening temperature of the shell 440 is lower than the thermal decomposition temperature of the blowing agent of the thermally expandable material 430 or the boiling point of the volatile liquid, the thermal decomposition temperature of the blowing agent of the thermally expandable material 430 or the boiling point of the volatile liquid is It will depend on the expansion of capsule 420.

Therefore, in this case, the expansion start temperature of the microcapsules 420 can be set by the material, composition, etc. of the thermally expandable substance 430.

Here, the expansion conditions of the microcapsules 420 will be explained for the former case, that is, the case where the temperature is higher than the softening temperature of the shell 440, the thermal decomposition temperature of the foaming agent of the thermally expandable material 430, or the boiling point of the volatile liquid.

In FIG. 4, if the inner diameter of the shell 440 is ``, the specific gravity of the thermally expandable material 430 contained is ρ, and the molecular weight is M, then the internal pressure P is P-((4πr''/3) ρ/MI X22.4
XIO3/(4πr''/3)-22,4X103ρ/M, and is independent of the shape of the shell 440.

Therefore, if the film thickness of the shell 440 is t1 and the vertically upward force applied to the hemisphere of the shell 440 is F, then (margin) F=fo ”2 P sinθ X2yrcosθ
X r dθ−πr2P If the elastic limit stress of the shell 440 at a certain temperature is σ, and the atmospheric pressure is PO, the conditions for the shell 440 to expand are F−yr (r + t) 2Pa 〉πf(r+t) 2 −r21 σ −π(2r+t)tσ, that is, P>((r+t) 2P6 + (2r+t)tσ)yr2.

Therefore, when the shell 440 softens due to temperature rise and the elastic limit stress σ decreases, microcapsules with a larger inner diameter r of the shell 440 are more likely to expand, and the thinner the shell 440 is, the more the microcapsules expand. easy.

In the latter case, that is, when the softening temperature of the shell 440 is lower than the thermal decomposition temperature of the blowing agent of the thermally expandable material 430 or the boiling point of the volatile liquid, P> ((r+t) 2PO + (2r+t)tσ)/ The internal pressure P at [2] changes greatly, and as in the former case, microcapsules with a larger inner diameter r of the shell 440 are more likely to expand, and the thinner the film thickness t of the shell 440 is, the easier it is to expand. .

The conditions for expanding the microcapsules 420 described above will be further explained using FIG. 5.

FIG. 5 shows a cross-sectional view of the microcapsule 420, and FIG.
b) Two types of microcapsules 420c whose shells 440 have different inner diameters r.

420d, and the same figure (C) shows two of the same shape made of different materials.
This figure shows different types of microcapsules 4'20e and 420f.

Microcapsule 420 a 54 shown in FIG. 5(a)
20b, the microcapsule 420a with a thin shell 440 has a thickness t, and in the microcapsules 420c and 420d shown in FIG. 5(a), the microcapsule 420d with a large inner diameter r expands at a low temperature.

Furthermore, even if the shape is the same as shown in FIG. When the temperature at which the elastic limit stress σ changes differs depending on the material, the expansion temperature also differs. For example, when polyvinylidene chloride, which is a copolymer of vinylidene chloride and acrylonitrile, is used as the shell material, shells with different expansion temperatures can be formed by changing the ratio of vinylidene chloride and acrylonitrile.

As a specific example, a shell containing 8 parts to 2 parts of vinylidene chloride and acrylonitrile will have an initial expansion temperature of about 20 to 25 degrees Celsius lower than a shell containing 5 parts to 5 parts of vinylidene chloride.

By manipulating the shape or material in this manner, microcapsules 420 having different expansion temperatures can be formed. By encapsulating these multiple types of microcapsules 420 in the same ink ribbon 400, it is possible to control the degree of expansion of the microcapsules 420 according to the amount of heating by the thermal head 360, and gradation recording is possible. Become.

Thermal expansion material 430 encapsulated in microcapsules 420
As mentioned above, a thermally decomposable blowing agent or a volatile liquid with a low boiling point is used, but as a blowing agent, a blowing agent compound that generates gas by thermal decomposition, which is commonly used in fields such as resin processing, is used. can also be used in the present invention. Further, as the volatile liquid, an evaporative/volatile blowing agent compound commonly used in fields such as resin processing can be used.

Microcapsules 420 containing a foaming agent can be obtained by a known microencapsulation method. For example, in the case of an aqueous solution type, there is a spray drying method in which a non-aqueous blowing agent is dispersed in the form of a suspension or emulsion in an aqueous solution that becomes a shell material, and the dispersion obtained is spray-dried, a phase separation method, a bombrex core, etc. Examples include cervation method, interfacial polymerization method, and in 5 situ polymerization method.

Microcapsule 420 containing a low boiling point volatile liquid
There are two types: one is a low boiling point volatile liquid itself, and the other is one in which resin particles are impregnated with a low boiling point volatile liquid. When a low boiling point volatile liquid itself is encapsulated, it can be obtained by a known microencapsulation method. For example, in the case of an aqueous solution type,
The spray drying method involves spray drying a dispersion obtained by dispersing a low-boiling point volatile liquid (insoluble in water) in the form of a suspension or emulsion into an aqueous solution that serves as a shell substance.Other methods include the phase separation method and the Pombrex core cell. Examples include vation method, interfacial polymerization method, etc.
This is disclosed in detail in Publication No. 24, etc.

In addition, when impregnating fine particles of resin, for example, a method of adding a volatile liquid during suspension polymerization of a suitable monomer (Japanese Patent Publication No. 33-3190), or a method of adding a volatile liquid during suspension polymerization of a suitable monomer, or a method of adding a volatile liquid to the particles obtained by suspension polymerization, etc. For example, there is a method in which a volatile liquid is added after swelling with water (Japanese Patent Publication No. 36-10628). Also,
If necessary, there is a method in which the resin is made fine and then impregnated with a volatile liquid.

The ink ribbon 400 in the present invention can be obtained, for example, by a known hot melt coating method or solvent coating method. In the hot-melt coating method, microcapsules 42 encapsulating a thermally expandable substance 430 are added to a coating liquid containing the above-mentioned binder and colorant as main components, which is obtained under heating.
0 is dispersed at a temperature and condition below the expansion start temperature to prevent thermal expansion, a coating liquid containing the microcapsules 420 to form the heat-melting ink layer 410 is prepared, and this is dispersed at a temperature and condition below the expansion start temperature. Apply using a bar coater etc.
Obtained by drying.

In the solvent coating method, microcapsules 420 encapsulating the thermally expandable substance 430 are dispersed in a coating solution containing a binder and a coloring material as main components dissolved in a solvent, and the microcapsules 420 encapsulating the thermally expandable substance 430 are dispersed in a coating solution containing a binder and a colorant dissolved in a solvent. to create a coating liquid containing the heat-melting ink layer 410,
This can be obtained by applying this using a bar coater or the like and drying it.

Further, in the above-described ink ribbon 400, only the case where the heat-melting ink layer 410 formed on the base film 450 is one layer has been described, but it may have a multilayer (two or more layers) structure as necessary. You can also do it.

Next, the principle of printing will be explained in detail using a schematic cross-sectional view of the recording paper P1 ink ribbon 400 and the thermal head 360 shown in FIG. In this example, the conveying speed of the ink ribbon 400 will be explained as 0.5 times the circumferential speed of the drum.

First, when the heating resistor of the thermal head 360 is energized, Joule heat is generated there, and the heat is transmitted to the heat-fusible ink layer 410 via the base film 450 of the ink ribbon 400 (FIG. 4(a)).

Next, the heat melts the heat-melting ink layer 410 and turns it into ink, and the microcapsules 420 expand to increase the volume of that portion. As a result, the melted ink of the heat-melting ink layer 410 is ejected from the surface of the ink ribbon 400 and is pressed against the uneven surface of the recording paper P (FIG. 4(b)). Since the ink ribbon 400 is being conveyed at a speed 0.5 times that of the recording paper P, the ink is stretched and attached to the surface of the recording paper P after one line period (FIG. 4(C)). As time passes further, the ink causes cohesive failure at the expanded microcapsules 420, and a pixel equivalent to one pixel is formed on the surface of the recording paper. Furthermore, most of the microcapsules 420 remain in the ink ribbon 400 because they are blocked by the unmelted heat-fusible ink layer 410 (FIG. 4(d)).

Here, by dispersing multiple types of microcapsules 420 with different expansion temperatures in the heat-melting ink layer 410 and controlling the energy applied to the thermal head 360,
Microcapsules 420 can be selectively expanded. Therefore, the degree of expansion of volume in the state shown in FIG. 6(b), that is, the ejection of ink! (Ink adhesion to the recording paper P![) can be changed, and gradation recording can be realized.

In addition, in the ink ribbon of this example, the case where the microcapsules are dispersed so as to be in contact with the base film (Fig. 3) was presented, but in
As shown in Figures (a) to (c), the particles may be dispersed (including protruding) in a floating state within the heat-melting ink layer without contacting them.

In the above description, these are examples presented, and the present invention is not limited thereto.

[Effects of the Invention] According to the present invention, the thermally expandable particles contained in the transfer surface are
Since there are multiple types of thermally expandable particles having different expansion start temperatures, the number of thermally expandable particles that expand changes depending on the temperature when heated, and the amount of ink extruded changes. Therefore, by changing the energy applied to each pixel, it is possible to control the print density and perform gradation recording.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure of an image forming apparatus according to an embodiment of the present invention, FIG. 2 is a sectional view showing the structure of a monochrome printing mechanism, and FIGS. 3(a) to 3d) are the structure of an ink ribbon. 4 is a perspective view showing the structure of the microcapsule, FIG. 5 (a) to C) is a sectional view of the microcapsule with different expansion conditions, and FIG. 6 (a) to d)
7(a) to 7(c) are diagrams showing microcapsules suspended in a heat-melting ink layer. DESCRIPTION OF SYMBOLS 10... Image forming apparatus, 300... Monochrome printing mechanism, 360... Thermal head, 400...
Ink ribbon, 410... hot melt ink layer, 420
... Microcapsule, 430 ... Thermal expansion material. Applicant: Toshiba Corporation Toshiba Intelligent Technology Co., Ltd. Agent: Patent Attorney Sadan Suyama Diagram (a) Schematic Diagram Diagram

Claims (4)

[Claims] (1) In a thermal transfer material provided with a transfer surface containing thermally expandable particles consisting of a shell and a thermally expandable material contained in the shell, the thermally expandable particles are formed in a plurality of layers having different softening start temperatures of the shell. A heat-sensitive transfer material characterized by being composed of a substance. (2) In a thermal transfer material provided with a transfer surface containing thermally expandable particles consisting of a shell and a thermally expandable material contained in the shell, the thermally expandable particles are composed of a plurality of materials whose shells have different thicknesses. A heat-sensitive transfer material comprising: (3) In a thermal transfer material provided with a transfer surface containing thermally expandable particles consisting of a shell and a thermally expandable substance contained in the shell, the thermally expandable particles are composed of a plurality of types having different inner diameters of the shells. A heat-sensitive transfer material characterized by: (4) In a thermal transfer material provided with a transfer surface containing thermally expandable particles consisting of a shell and a thermally expandable substance contained in the shell, the thermally expandable particles have a specific gravity and a molecular weight of the thermally expandable substance. A thermal transfer material characterized by being composed of multiple types with different ratios.