JPH11208109A - Image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming method capable of raising the sensitivity of transfer and obtaining stable images irrespective of lapse of time of an image receiving sheet. SOLUTION: The image forming method is such that a heat-transferable heat-melt ink layer is thermally transferred on the image receiving sheet to form transfer images in a transfer sheet, wherein the image receiving sheet is preheated in advance higher than the glass transition temperature (Tg) of a binder used in the uppermost layer of the image receiving sheet, and after being cooled, it is melted thermally. For this operation, e.g. before the heat-melt ink layer is transferred on the image receiving sheet, an image receiving sheet heating roller is controlled in temperature higher than Tg+10 deg.C of the binder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method, and more particularly, to a method in which a heat transferable sheet having a heat fusible ink layer is combined with an image receiving sheet to thermally transfer the heat fusible ink layer of the heat transfer sheet to the image receiving sheet. The present invention relates to an image forming method for forming an image.

[0002]

2. Description of the Related Art In recent years, with the progress of OA, image formation using an image forming apparatus such as a copying machine or a printer has been widely performed. In the image formation, various recording methods such as an electrophotographic method, an ink jet method, and a thermal transfer recording method are used. Among them, the operation and maintenance are easy, and the apparatus can be reduced in size and cost. Due to such advantages as described above, the thermal transfer recording system has been particularly noted. For the heat-sensitive transfer layer of the transfer sheet used in the heat-sensitive transfer recording method, a coloring material is used, and in general, a composition containing the coloring material is softened or melted, or the coloring material is evaporated or sublimated,
An image is formed on an image receiving sheet such as a paper or a film sheet by the action of adhesion, adsorption, dyeing or the like.

In the image receiving sheet used in these image forming methods, if the aging time of the image receiving sheet becomes long,
When the image is formed by thermally transferring the heat-meltable ink layer of the thermal transfer sheet to the image-receiving sheet in combination with the heat-transfer sheet having the heat-meltable ink layer using the image-receiving sheet, the transfer of the heat-meltable ink layer from the heat-transfer sheet is performed. Sensitivity tends to decrease gradually.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming method capable of improving transfer sensitivity and stabilizing an image irrespective of time.

[0005]

According to the present invention, as the aging time of the image-receiving sheet becomes longer, the transfer sensitivity of the heat-meltable ink layer from the thermal transfer sheet gradually decreases because the binder in the uppermost layer of the image-receiving sheet is aging. When the relaxation phenomenon progresses, the free volume in the binder decreases and the mobility of the molecules decreases, so when it is used for a thermal transfer material using a thermal head, it is very remarkable. This was achieved as a result of paying attention to the fact that the movement of the binder could not follow the heat and the apparent decrease in the transfer sensitivity was observed. That is, the present invention relates to an image forming method for thermally transferring a thermally fusible ink layer on a transfer sheet onto a receiving sheet to form a transfer image, wherein the binder glass used as the uppermost layer of the receiving sheet is used. The image forming method is characterized in that the image receiving sheet is preliminarily heated to a transition temperature (Tg) or higher, cooled, and then the heat-fusible ink is transferred onto the image receiving sheet. Therefore, according to the present invention, if the image receiving sheet is preliminarily heated to a temperature equal to or higher than the glass transition temperature (Tg) of the binder used for the uppermost layer of the image receiving sheet, then the temperature of the binder in the uppermost layer of the image receiving sheet becomes higher. Even when cooled to room temperature, the effect of improving the transfer sensitivity is maintained.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The image receiving sheet usually has an image receiving layer on one surface of a support, and optionally has a back layer on the other surface. The image receiving layer comprises an image receiving layer exposed on the surface of the image receiving sheet and an intermediate layer not exposed on the surface of the image receiving sheet, and further has other layers as necessary. In this case, the intermediate layer may be referred to as a first image receiving layer, and the image receiving layer exposed on the surface of the image receiving sheet may be referred to as a second image receiving layer.

In an image forming method by thermal transfer, an image receiving layer of the above image receiving sheet and a heat transferable heat fusible ink layer of the transfer sheet are overlapped with each other, and a thermal head, laser or the like is used to transfer the heat transferable image of the transfer sheet. The hot melt ink layer is heated imagewise. At this time, the heat-meltable ink layer heated imagewise is separated from the thermal transfer sheet and transferred to the image receiving layer surface exposed on the surface of the image receiving sheet, thereby forming an image. In the present invention, it is necessary that the image receiving sheet does not substantially contain a compound having a hardening effect. Compounds having a substantially hardening effect include, for example, compounds such as polyaldehydes, polyvalent isocyanates, epoxy compounds and divinyl sulfone. The image-receiving sheet of the present invention comprises these compounds in the uppermost layer and / or the intermediate layer. It means an image receiving sheet not having a layer. When a compound having a substantially hardening effect is contained in the uppermost layer and / or the intermediate layer, the hardening reaction of the image receiving layer proceeds by preheating, and the glass transition temperature (Tg) of the binder increases. The transfer sensitivity of the hot-melt ink layer from the thermal transfer sheet is lowered, which is not preferable.

In the present invention, the image receiving sheet is preheated before performing the above-described thermal transfer. This preheating temperature is determined by the glass transition temperature (T.sub.T) of the binder used in the uppermost layer (image receiving layer or second image receiving layer) of the image receiving sheet.
g) or more. However, the binder used in the uppermost layer of the image receiving sheet is not limited to one kind, and may be two or more kinds. In this case, the preheating temperature is set to the glass transition temperature (two or more kinds of binders). Tg) is a temperature equal to or higher than the higher Tg.

When the preheating temperature is lower than the glass transition temperature (Tg) of the binder, the state in which the relaxation phenomenon of the binder continues, that is, the free volume of the binder decreases, and the mobility of the molecule decreases. Because of this state, the movement of the binder cannot follow sudden heat during the fusion thermal transfer using the thermal head, and apparently the transfer sensitivity is reduced.

Although the transfer sensitivity is improved even when the preheating temperature is increased and excessive heat is applied to the image receiving sheet, if the preheating temperature is too high, the image receiving layer of the image receiving sheet is melted. Therefore, the preheating temperature should be a temperature that is equal to or higher than the glass transition temperature (Tg) of the binder and does not cause the above-mentioned adverse effects.

As a method for preheating the image receiving layer of the image receiving sheet, for example, there is no particular problem with heating using an oven or the like, but a step of heating the image receiving sheet via a heating roller in a step before thermal transfer is desirable. The heating roller may be incorporated in the printer, or may exist as a separate unit from the printer.

In this case, the temperature of the image receiving sheet is adjusted by the temperature of the heating roller and the time during which the image receiving sheet contacts the heating roller. Therefore, the temperature of the heating roller is
At least the uppermost layer of the image receiving sheet (the image receiving layer or the second layer
It is necessary that the temperature is higher than the glass transition temperature (Tg) of the binder used in the image receiving layer), but when the temperature of the heating roller is near the glass transition temperature (Tg) of the binder, the image receiving sheet is brought into contact with the heating roller. The time for performing the heat transfer is too long, and the production efficiency of the thermal transfer process is undesirably reduced.

Therefore, in the step of heating the image receiving sheet via the heating roller in a step before the thermal transfer, the temperature of the heating roller is used for the uppermost layer (image receiving layer or second image receiving layer) of the image receiving sheet. The glass transition temperature (Tg) of the binder is preferably + 10 ° C. or higher.

It is desirable that the temperature of the image receiving sheet is cooled to an ambient temperature at which the thermal transfer step is performed during the period from the preheating to the thermal transfer step. If the thermal transfer step is performed while the temperature of the image receiving sheet is higher than the ambient temperature, the transfer sensitivity is improved, but the degree of improvement is not stable, which is not preferable. The time from the pre-heating to the thermal transfer step can be appropriately selected within a time sufficient for the temperature of the image receiving sheet to be cooled to the ambient temperature. However, if the time is too long, the relaxation phenomenon of the binder proceeds again, and the transfer sensitivity is lowered. It is not preferable because re-drop occurs. Specifically, from the preheating to the thermal transfer process, 2
It is preferably within 4 hours, more preferably within 2 hours.
If the heating roller is placed inside the printer, the time from preheating to the thermal transfer step can be used to reduce the total printing time if it is sufficient to allow the image receiving sheet to cool to room temperature. It is preferable that is shorter.

Next, the image receiving sheet and the thermal transfer sheet applied to the image forming method of the present invention are not particularly limited, and any known ones can be used. These sheets will be described. Examples of the support in the image receiving sheet include substances that are chemically and thermally stable and have flexibility. Specific examples include polyolefins such as polyethylene and polypropylene, polyvinyl chloride, and polyvinylidene chloride. And cellulose derivatives such as cellulose acetate, nitrocellulose, and cellophane, polyamides, polystyrene, polycarbonate, polyimides, and, in some cases, paper laminated with a polyethylene film. These may be used alone or in combination of two or more.

In the present invention, among these, a biaxially stretched polyethylene phthalate film excellent in dimensional stability and permeability is particularly preferred. In the present invention, a plastic sheet having microbubbles inside is preferable in terms of heat insulation and cushioning property, and specifically, a foamed polyolefin film, a foamed polyester film, and the like are preferable. In the present invention, the material of the support may be transparent to actinic rays, if necessary.

Intermediate layer in image receiving sheet (first image receiving layer)
Examples thereof include polyolefins such as polyethylene and polypropylene, ethylene copolymers such as ethylene-vinyl acetate copolymer and ethylene-acrylate copolymer, polyvinyl chloride, and chlorides such as vinyl chloride-vinyl acetate copolymer. Vinyl copolymer, polyvinylidene chloride, vinylidene chloride copolymer, poly (meth) acrylate,
Examples thereof include polyamide resins such as copolymerized nylon and N-alkoxymethylated nylon, and organic polymer substances such as synthetic rubber and chlorinated rubber. These may be used alone or in combination of two or more.

In the present invention, among the materials for the intermediate layer, polyvinyl chloride, a vinyl chloride-vinyl acetate copolymer, a vinyl chloride
Vinyl alcohol copolymer, vinyl chloride / vinyl acetate
Vinyl chloride copolymers such as maleic acid copolymers are particularly preferred. The polyvinyl chloride and the vinyl chloride copolymer have (1) almost no tackiness at room temperature, (2) a relatively small elastic modulus, and can easily follow irregularities of a transferred image during thermal transfer. (3) A substantial amount of a plasticizer having good compatibility is abundant, and substantial control of the elastic modulus is easy. (4) The effect of the hydroxyl group or carboxyl group in the copolymer component is easy to control the interlayer adhesion. And so on.

When a vinyl chloride resin such as the polyvinyl chloride or the vinyl chloride copolymer is used as the material of the intermediate layer, butyl known as a stabilizer for the vinyl chloride resin is contained in the intermediate layer. An organic tin stabilizer such as a tin stabilizer and an octyltin stabilizer may be added.

The intermediate layer preferably has an appropriate cushioning property. When the first image receiving layer has an appropriate cushioning property, it is advantageous in that the recording sensitivity, dot quality, and gradation reproducibility are improved. For this reason, if the material of the selected intermediate layer alone is insufficient in cushioning properties, a plasticizer is added to the intermediate layer within a range that does not impair the object of the present invention in order to supplement the cushioning properties of the intermediate layer. can do.

The plasticizer is not particularly limited as long as the object of the present invention is not impaired, and can be appropriately selected from known ones. However, a plasticizer which hardly migrates from the intermediate layer to the outside is preferable. As such a plasticizer, for example,
Examples thereof include polyester-based and urethane-based oligomers. These may be used alone or in combination of two or more, or commercially available products may be used.

Examples of the polyester type include adipic acid type, phthalic acid type, sebacic acid type, epoxy type,
Trimellitic acid, pyromellitic acid, citric acid and the like can be mentioned. Among these, adipic acid type, phthalic acid type, sebacic acid type and the like are preferable. The urethane oligomer is preferably a general copolymer of isocyanate with polyether diol or polyester diol, or an oligomer of aromatic urethane acrylate or aliphatic urethane acrylate.

The molecular weight of the plasticizer is not particularly limited and can be appropriately selected according to the purpose.
00 or more is preferable. If the molecular weight of the plasticizer is less than 1,000, the plasticizer tends to migrate to the surface of the image receiving layer, and the surface of the image receiving layer becomes sticky, which may cause problems such as staking and dust defects.

The thickness of the intermediate layer is 1 to 50 μm
Is preferably, and particularly preferably 5 to 30 μm. When the thickness of the intermediate layer is within the preferred numerical range, the thickness of the intermediate layer is larger than the irregularities on the surface of the permanent support for re-transferring the image transferred from the transfer material onto the image receiving sheet material. Is good, and the relief step at the portion where the four color images overlap can be sufficiently absorbed, and sufficient cushioning properties can be obtained.

Examples of the cushioning of the intermediate layer, the Young's modulus is preferably about 10~10000kg · f / cm ² at room temperature, about 10~200kg · f / cm ² is more preferable. When the Young's modulus is within the above numerical range, an appropriate cushioning property is generated in the image receiving layer, and the recording sensitivity, dot quality, tone reproducibility, and the like of the image receiving sheet material can be improved. In addition, when an image is formed, even if a foreign substance such as dust exists between the recording material and the image receiving sheet material, the intermediate layer has an appropriate cushioning property, so that an image defect hardly occurs. Also,
After transferring the image to the image receiving sheet, when re-transferring to the printing paper such as paper by heat and pressure, because the intermediate layer is embedded according to the unevenness of the paper, the adhesion with the printing paper such as paper is good, An image having a surface gloss similar to a printed matter is obtained.

Image receiving layer (second image receiving layer) in image receiving sheet
Constitutes the uppermost layer of the image receiving sheet. The image receiving layer contains a binder, a matting agent, an antistatic agent, a surfactant, and the like.In addition, in order to impart film forming properties, heat resistance, light resistance, film strength, water repellency, lubricity, etc., silicone is used. Compounds may be added.

The binder in the present invention is a general term for components which substantially function as a binder in the image receiving layer. That is, in addition to a binder in a pure sense, what is called a thermosoftening resin is also included.

The binder is not particularly limited and can be appropriately selected from known binders. Examples thereof include polyolefins such as polyethylene and polypropylene, ethylene / vinyl acetate copolymers, and ethylene / acrylate copolymers. , Ethylene copolymer such as ethylene-acrylic acid copolymer, polyvinyl chloride, vinyl chloride
Vinyl chloride copolymer such as vinyl acetate copolymer, polyvinylidene chloride, vinylidene chloride copolymer, polystyrene,
Styrene copolymers such as styrene / maleic acid ester copolymers, vinyl acetate copolymers, modified polyvinyl alcohol, polyamide resins such as copolymerized nylon, N-alkoxymethylated nylon, synthetic rubber, chlorinated rubber, phenolic resin, epoxy Resin, urethane resin, urea resin, melamine resin, alkyd resin, maleic acid resin, hydroxystyrene copolymer, sulfonamide resin, ester gum, cellulose resin, rosin and the like. These may be used alone or in combination of two or more, and may be appropriately synthesized or commercially available products.

The heat-softening resin which also functions as a binder has a glass transition point (softening point) of at most 150 ° C.
The resin has a glass transition point (softening point) of preferably -20 to 150 ° C, more preferably 15 to 120 ° C, and more preferably 35 to 100 ° C.
Is particularly preferred.

When the glass transition point exceeds 150 ° C., the thermal recording sensitivity decreases, and when the glass transition point is lower than −20 ° C., the adhesion resistance of the image receiving layer may deteriorate. On the other hand, if the glass transition point is within the preferred numerical range, it is advantageous in the above point, and if it is in the more preferred numerical range, it is more advantageous in image quality. The glass transition point is, for example,
It can be measured by a differential scanning calorimeter (DSC) or the like.

Examples of the heat-softening resin include amorphous organic polymer binders having the glass transition point within the above-mentioned numerical range, and more specifically, for example, polyvinyl butyral, polyamide, Polyethyleneimine,
Sulfonamide, polyester polyol, petroleum resin,
Styrene, vinyltoluene, α-methylstyrene, 2-
Styrene such as methylstyrene, chlorostyrene, vinylbenzoic acid, sodium vinylbenzenesulfonate, aminostyrene and derivatives thereof, homopolymers and copolymers of substituted products, methyl methacrylate, ethyl methacrylate, butyl methacrylate, hydroxyethyl methacrylate, etc. Methacrylic acid esters and acrylic acid esters such as methacrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, α-ethylhexyl acrylate and dienes such as acrylic acid, butadiene and isoprene, acrylonitrile, vinyl ethers, maleic acid and maleic acid esters And homopolymers of vinyl monomers such as maleic anhydride, cinnamic acid, vinyl chloride and vinyl acetate, and copolymers with other monomers. These may be those obtained by modifying the hydroxyl group of the binder with an isocyanate compound or the like in order to improve the effect of humidity. In addition, these may be used alone or in combination of two or more, and may be appropriately synthesized one, or may be a commercially available one.

Among them, polyvinyl butyral,
Styrene / maleic acid half ester resin and derivatives thereof are preferred, and polyvinyl butyral and derivatives thereof are particularly preferred. The use of polyvinyl butyral and its derivatives as the heat-softening resin is advantageous in terms of thermal adhesion to the hot-melt ink layer.

The polyvinyl butyral is a resin obtained by acetalizing (butyralizing) polyvinyl alcohol with butyl aldehyde using an acid catalyst, and may be appropriately synthesized or a commercially available product. The molecular weight of the polyvinyl butyral and its derivative is not particularly limited as long as the object of the present invention is not impaired, but is preferably, for example, about 500 to 50,000.

The thickness of the image receiving layer is 0.1 to 10
μm is preferred, and 0.5 to 5 μm is particularly preferred. If the thickness is less than 0.1 μm, poor transfer may occur during transfer to the printing paper or the image quality of the transferred image may be degraded. If it exceeds 10 μm, the surface of the permanent support may have unevenness. In the case of proof use, glossiness may be too high, and the printed matter approximation may be deteriorated.

Therefore, the glass transition temperature (Tg) of the binder in the image forming method of the present invention means the glass transition temperature (Tg) of a heat-softening resin or the like which functions as a binder in addition to the binder itself. The image forming method of the present invention is to preheat to a temperature of the highest Tg or higher among these components contained in the image receiving layer.

The image-receiving sheet according to the present invention may further comprise an undercoat layer for improving the adhesive force between the support and the intermediate layer (first image-receiving layer), and an adhesive layer between the image-receiving layer and the intermediate layer. It may have a release layer for improving the releasability, transferability, etc. of the toner, or may have a back layer on the surface of the support opposite to the surface on which the image receiving layer is provided.

The thermal transfer sheet according to the present invention has a heat-fusible ink layer capable of being thermally transferred on a support, and if necessary, a release layer, a heat-fusible ink layer between the support and the heat-fusible ink layer.
It may have a layer having various functions such as a barrier layer and a cushion layer. The transfer sheet is not particularly limited as long as the heat-fusible ink layer as the image forming layer has a function of being peeled off from the support by being imagewise heated and transferred to the image receiving sheet. Instead, it can be appropriately selected according to the purpose.

The heat-transferable heat-meltable ink layer contains at least a pigment and a heat-softening resin, and other components are not particularly limited, and include various polymers, adhesion improvers, and surfactants. Any known additive such as a release agent can be used in a range that does not impair the purpose of the present invention, specifically, about 1 to 15 parts by weight.

For example, various release agents and softeners are melted in the ink layer from the viewpoint of improving the releasability from the support and the thermal sensitivity of the heat-meltable ink layer during thermal printing. You may add 1-20 weight% with respect to the ink layer total amount. More specifically, for example, higher fatty acids such as palmitic acid and stearic acid; fatty acid metal salts such as zinc stearate; fatty acid esters or partially saponified products thereof; fatty acid derivatives such as fatty acid amides; higher alcohols; Ester derivatives of alcohols, paraffin wax, carnauba wax, montan wax, beeswax, wood wax,
Waxes such as candalia wax, low molecular weight polyethylene having a viscosity average molecular weight of about 1,000 to 10,000, polyolefins such as polypropylene, polybutylene or olefins, α-olefins and maleic anhydride, acrylic acid, methacrylic acid Organic acids such as, low molecular weight copolymers such as vinyl acetate, low molecular weight oxidized polyolefin, halogenated polyolefins, lauryl methacrylate, stearyl methacrylate, methacrylic acid ester having a long alkyl side chain such as stearyl methacrylate, acrylic acid ester or Low molecular weight silicone resins such as acrylic acid esters and methacrylic acid esters having a perfluoro group alone or copolymers with vinyl monomers such as styrenes, polydimethylsiloxanes and polydiphenylsiloxanes And silicone-modified organic substances, and further, a cationic surfactant such as an ammonium salt or a pyridinium salt having a long-chain aliphatic group, or an anion having a long-chain aliphatic group, a nonionic surfactant, or a perfluoro-based surfactant. An activator or the like may be added. As the other components, one kind may be used alone, or two or more kinds may be used in combination.

The thickness of the hot-melt ink layer is, for example, 0.2 to 1.0 μm, and 0.2 to 0.8 μm.
Is preferably, and more preferably 0.3 to 0.6 μm. If the thickness of the heat-fusible ink layer is less than 0.2 μm, it may be difficult to obtain a predetermined concentration,
When the value exceeds, the shadow portion is easily crushed in the tone reproducibility based only on the area tone, and the highlight portion is liable to fly, resulting in poor tone reproducibility. The heat-transferable heat-meltable ink layer is formed so as to be melted or softened at the time of thermal transfer so as to be peelable and transferable from the support.

The pigment is not particularly limited and may be appropriately selected from various known pigments. Examples thereof include carbon black, azo-based, phthalocyanine-based, quinacridone-based, thioindigo-based, and anthra-based pigments. Quinones and isoindolines are preferred. These may be used alone or in combination of two or more, and a known dye may be used in combination for adjusting the hue. In the present invention, the thermal transfer may be performed using a thermal head or using a laser.

[0042]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to these examples. (Preparation of Image Receiving Sheet) Coating solutions for the single image receiving layer and the two image receiving layers having the following compositions were prepared. (Coating solution for one image receiving layer) Binder Vinyl chloride / vinyl acetate copolymer (Solvain CL2, manufactured by Nissin Chemical Co., Ltd.) 160 parts by weight Ethylene / vinyl acetate copolymer (Elvaloy 742, DuPont Mitsui Chemicals, Inc.) 61 parts by weight ・ Plasticizer FN-G25 (manufactured by Nippon Soda Co., Ltd.) 28 parts by weight ・ Surfactant (Megafax F-113) 2 parts by weight ・ Surfactant (Megafax F-178K) 2 parts by weight Dainippon Ink and Chemicals, Inc.) Solvent Methyl ethyl ketone 630 parts by weight Toluene 210 parts by weight Dimethylformamide 30 parts by weight

(Coating solution for two-layer image receiving) Binder butyral resin A (Tg: 58 ° C.) 13 parts by weight (trade name BL-SH, manufactured by Sekisui Chemical Co., Ltd.) Binder butyral resin B (Tg: 66 ° C.) 71 parts by weight (modified product of cyclohexyl isocyanate of BL-SH: 70% conversion rate) Surfactant (trade name: Megafax F-176PF 0.6 parts by weight, manufactured by Dainippon Ink and Chemicals, Inc.) Solvent Methanol 630 parts by weight Parts n-propyl alcohol 30 parts by weight

On a support of a white polyethylene terephthalate (PET) film (trade name: E-68L, manufactured by Toray Industries, Inc.) having a thickness of 130 μm, the above-mentioned coating solution for image receiving layer was applied at 300 rpm by using a rotary coating machine (Woerler). Apply with 1
It was dried in an open at 00 ° C. for 2 minutes. The thickness of the obtained image receiving layer was 20 μm. On the one image receiving layer, the coating solution for the two image receiving layers was applied at 200 rpm using a rotary coating machine (Woerr) and dried in an oven at 100 ° C. for 2 minutes. The film thickness of the obtained two image receiving layers was 2 μm.

<Evaluation of Transfer Sensitivity> A thermal transfer sheet was prepared by the following method, and the transfer sensitivity of the toner was evaluated. (Preparation of Thermal Transfer Sheet) The following three types of coating solutions for ink layers were prepared. -Butyral resin 12 parts by weight (Denka Butyral # 2000-L, manufactured by Denki Kagaku KK)-Pigment ABC cyan pigment (CI, P, B, 15: 4) 12 parts by weight--Magenta pigment (C, I, P, R, 57: 1)-12 parts by weight-Yellow pigment (C, I, P, Y, 14)-12 parts by weight-Dispersant Solsperse S-20000 0.8 part by weight (manufactured by ICI Japan Co., Ltd.)・ Solvent n-propyl alcohol 110 parts by weight

To 10 parts by weight of each of the pigment dispersions of A, B, and C, 0.24 parts by weight of stearamide and 60 parts by weight of n-propyl alcohol were added to prepare a coating solution having a thickness of 5 μm.
m, a polyester film (manufactured by Toray Industries, Inc.) having a release treatment on its back side has a dry film thickness A of 0.36 μm and a film thickness of B of 0.38
A thermal transfer sheet was prepared by coating so that μm and C became 0.42 μm. First, a cyan thermal transfer sheet and an image receiving sheet were overlapped, and printing was performed by a thermal head recording apparatus (prototype experimental machine) using the sub-scanning division method. This principle is 75 μm ×
This is a method of performing multi-stage modulation of only area gradation by turning on and off a 50 μm head at a pitch of 3 μm by minute feed in the 50 μm direction. Peel this cyan thermal transfer sheet,
An image consisting only of area gradation was formed on the image receiving sheet. Next, the magenta thermal transfer sheet is superimposed on the image receiving sheet on which the cyan image is formed, printed in the same manner, and the transfer sheet is peeled off to form a magenta image and a yellow image on the image receiving sheet in the same manner. Then, a color image consisting only of the area gradation was formed on the image receiving sheet. The transfer sensitivity of the image thus formed was evaluated. The transfer sensitivity was determined by measuring the area ratio of the transferred halftone dots using a Macbeth densitometer.

<Stabilization of Sensitivity of Image-Receiving Sheet by Prethermo> The image-receiving sheet is placed in a moisture-proof bag, treated with a thermostat at 40 ° C. for 7 days, and then subjected to conditions for measuring the transfer sensitivity (23 ° C., 60 ° C.).
%), And a sample having a small change in sensitivity over time was prepared. <Improving the sensitivity of the image receiving sheet by preheating>

Example 1 An image receiving sheet was preheated in a dry oven at 70 ° C. for 5 minutes, and then conditioned for 1 hour to measure the transfer sensitivity of the toner. When transfer was performed at a printing energy of 50% of the dot area ratio after the transfer of the cyan toner on the image receiving sheet not subjected to the preheating treatment, the dot area ratio was 65%.
And a 15% increase in sensitivity was observed.

Example 2 A preheating treatment was carried out in the same manner as in Example 1 except that the toner to be transferred was changed from cyan to magenta, and the transfer sensitivity was measured. When transfer was performed with a printing energy of 50% of the dot area ratio after magenta toner transfer on the image receiving sheet that was not subjected to the preheating treatment, the dot area ratio was 66%, and a sensitivity increase of 16% was recognized. Was done.

Example 3 A preheating treatment was performed in the same manner as in Example 1 except that the toner to be transferred was changed from cyan to yellow, and the transfer sensitivity was measured. When transfer was performed with a printing energy of 50% of the dot area ratio after magenta toner transfer on the image receiving sheet not subjected to the preheating treatment, the dot area ratio was 63%, and the sensitivity was increased by 13%. Was done.

Example 4 A preheating treatment was performed in the same manner as in Example 1 except that the temperature of the preheating treatment was changed from 70 ° C. to 120 ° C., and the transfer sensitivity was measured. When transfer was performed with a printing energy of 50% of the dot area ratio after the transfer of the cyan toner on the image receiving sheet not subjected to the preheating treatment, the dot area ratio was 65%, and the sensitivity was increased by 15%. Was. It was confirmed that even when the temperature was excessively increased, the degree of sensitivity increase was stable.

Example 5 An image receiving sheet was sandwiched between aluminum guide plates provided with a release-treated film, and 100 c
After passing through the preheating treatment at a speed of m / min, the humidity was adjusted for 1 hour, and the transfer sensitivity of the toner was measured. When transfer was performed with a printing energy of 50% of the dot area ratio after transfer of the cyan toner on the image receiving sheet not subjected to the preheating treatment, the dot area ratio was 65%, and the sensitivity was increased by 15%. Was done.

Example 6 The temperature of the heating roller was 130 ° C. and the passing speed was 100 cm.
The transfer sensitivity was measured in the same manner as in Example 5, except that the preheating treatment was performed at a rate of / min. When transfer was performed with a printing energy of 50% of the dot area ratio after transfer of the cyan toner on the image receiving sheet not subjected to the preheating treatment, the dot area ratio was 65%, and the sensitivity was increased by 15%. Was done. As in Example 4, it was confirmed that the degree of sensitivity increase was stable even when heat was applied excessively.

Example 7 The temperature of the heating roller was 120 ° C., and the temperature of the heating roller was 200 cm /
The transfer sensitivity was measured in the same manner as in Example 5 except that the preheating treatment was performed at a minimum. When transfer was performed with a printing energy of 50% of the dot area ratio after transfer of the cyan toner on the image receiving sheet not subjected to the preheating treatment, the dot area ratio became 55%, and the sensitivity was increased by 5%. However, it is considered that the sensitivity increase was insufficient due to insufficient heat treatment.

Comparative Example 1 A preheating treatment was performed in the same manner as in Example 1 except that the temperature of the preheating treatment was changed from 70 ° C. to 50 ° C., and the transfer sensitivity was measured. When transfer was performed at a printing energy of 50% of the dot area ratio after transfer of the cyan toner on the image receiving sheet not subjected to the preheating treatment, the dot area ratio remained at 50%, and the sensitivity was increased. I couldn't.

Comparative Example 2 The temperature of the heating roller was 100 ° C., and the passing speed was 200 cm.
Example 5 except that the preheating treatment was performed at
The transfer sensitivity was measured in the same manner as described above. When transfer was performed with a printing energy of 50% dot area ratio after cyan toner transfer on the image receiving sheet that was not subjected to the preheating treatment,
The halftone dot area ratio remained at 50%, and no increase in sensitivity was observed. The temperature of the heating roller was 100 ° C.,
It seems that the contact time between the heating roller and the image receiving sheet was short and the binder in the image receiving layer was not sufficiently heated.

[0057]

As described above, according to the present invention, the image-receiving sheet is preliminarily heated to a temperature equal to or higher than the glass transition temperature (Tg) of the binder used for the uppermost layer of the image-receiving sheet, and is allowed to cool. By transferring the fusible ink onto the image receiving sheet, the transfer sensitivity of the toner can be increased, and a stable increase in sensitivity can be obtained.

Claims (2)

[Claims] An image forming method in which a thermally fusible ink layer capable of being thermally transferred on a transfer sheet is thermally transferred onto an image receiving sheet to form a transfer image, wherein a glass transition of a binder used as an uppermost layer of the image receiving sheet. An image forming method comprising: preliminarily heating an image-receiving sheet at a temperature (Tg) or higher, cooling the image-receiving sheet, and then transferring the heat-fusible ink onto the image-receiving sheet. 2. A heating roller for heating the image receiving sheet to a temperature equal to or higher than the glass transition temperature (Tg) of the binder used for the uppermost layer of the image receiving sheet before transferring the heat-fusible ink layer onto the image receiving sheet. 2. The image forming method according to claim 1, wherein the temperature is adjusted to Tg + 10 ° C. or higher.