JPH07164764A - Thermal transfer image receiving sheet - Google Patents

Abstract

PURPOSE:To provide a sublimation type thermal transfer receiving sheet imparting high print density and causing no density irregularity. CONSTITUTION:At least one coating layer containing pigment and a resin as main components is provided on one surface of a sheet like support and an image receiving layer receiving a thermal transfer image forming dye to be dyed is provided on the coating layer. The sheet like support is bulky paper with density of 0.15-0.5g/cm<3> obtained by foaming raw paper produced from pulp and foamable particles by a papermaking process under heating and, if necessary, at least one coating layer is subjected to cast coating processing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal transfer image receiving sheet (hereinafter abbreviated as image receiving sheet). More specifically, the present invention relates to an image-receiving sheet that receives an image-forming dye such as a sublimation dye that has been thermally transferred in a thermal (thermal recording) printer, particularly a sublimation-type thermal transfer printer, and that receives an image with high sensitivity. is there.

[0002]

2. Description of the Related Art In recent years, thermal transfer type high-quality color hard copy, especially sublimation type thermal transfer printer, has been rapidly developed. In a sublimation thermal transfer printer, an image receiving layer containing a dye-dyeable resin of an image receiving sheet is superposed on a sublimation dye ink sheet of three colors (yellow, magenta, cyan),
The heating energy of the thermal head is continuously controlled and heated according to the image pattern to change the transfer amount of the dye of each color, thereby making it possible to form a full-color image of density gradation.

In order to form a high quality printed image on an image receiving sheet at high speed by such a sublimation type thermal transfer printer, an image receiving layer containing a dye-dyeable resin as a main component is provided on a base material. When a paper such as coated paper or art paper is used as the base material of the image receiving sheet, it has a drawback that the sensitivity for receiving the dye for image formation is low because the thermal conductivity is relatively high.

Therefore, it is known to use a biaxially stretched film having a void as a main component of a thermoplastic resin such as polyolefin as a base material of an image receiving sheet. An image-receiving sheet using such a film as a base material has a uniform thickness, is flexible, and has a lower thermal conductivity than paper made of cellulose fibers, and thus has the advantage that a uniform and high-density image can be obtained. There is.

However, when such a biaxially stretched film is used as a base material of an image receiving sheet, uneven density of a printed image caused by a void structure existing on the surface is a problem. In addition, the residual stress during stretching is relaxed by the heat during printing, heat shrinks in the stretching direction, and as a result curls and wrinkles occur on the image receiving sheet, causing problems such as paper jams when traveling through the printer. Was becoming.

In order to improve these drawbacks, a laminate sheet in which biaxially stretched films are laminated and laminated on both surfaces of a core material having a relatively small heat shrinkage rate or a core material having a large elastic modulus is used as a base material of an image receiving sheet. It is known. But,
Since the sheets having different heat shrinkage rates are laminated, curling occurs due to the difference in shrinkage rate between both layers, and the cost is significantly increased.

There is also known a method in which a heat insulating layer or a cushion layer is provided on a base material so that the printer head is brought into uniform contact with the sheet to prevent low density and white spots. In the case of (1), the cost is increased by increasing the number of steps by one step, and the problem of paper jam cannot be solved sufficiently. JP-A-2-263691 describes the use of expanded polypropylene as a substrate for the same effect. However, a sheet-like support mainly composed of pulp and having high heat insulation has not been reported yet.

[0008]

SUMMARY OF THE INVENTION The present invention has the drawbacks of the prior art, that is, the sensitivity is lowered when a coated paper is used as a support and the density unevenness is caused when a void-containing biaxially stretched film is used. It is an object of the present invention to provide a thermal transfer image-receiving sheet that has been solved, is inexpensive, has high print density, and has excellent image quality.

[0009]

DISCLOSURE OF THE INVENTION The inventors of the present invention have earnestly studied to obtain an image-receiving sheet suitable for receiving a print image of excellent quality, and as a result, the pulp having a specific density as a support of the image-receiving sheet. The present invention has been completed by finding that the above-mentioned problems can be solved by using a foamed porous bulky paper as a main component.

That is, the thermal transfer image-receiving sheet according to the present invention comprises a sheet-like support, at least one coating layer formed on one surface of the sheet-like support and containing a resin as a main component, and the above-mentioned coating. Formed on the layer, having an image receiving layer for receiving and dyeing a thermal transfer image forming dye, the sheet-shaped support is made into a papermaking slurry containing pulp and expandable particles, the obtained base paper Is a bulky paper obtained by foaming by heating and having a density of 0.15 to 0.5 g / cm ³ .

At least one of the coating layers used in the present invention
It is preferable that the layer is formed by cast coating in which a coating layer formed of a coating liquid composition containing a pigment and a resin as a main component is pressed against the surface of a heating drum to give a gloss finish.

[0012]

The bulky paper used for the sheet-like support of the thermal transfer image-receiving sheet of the present invention and having a density of 0.15 to 0.5 g / cm ³ includes pulp and a core substance composed of a low boiling point liquid, It is obtained by forming a mixed paper slurry containing expandable particles composed of an outer shell containing the paper, and heating the obtained sheet to foam.

The pulp used in the present invention is not particularly limited. For example, wood pulp such as chemical pulp and mechanical pulp of softwood and hardwood, waste paper pulp, non-wood natural pulp such as hemp and cotton, polyethylene, polypropylene and the like. It is possible to use a synthetic pulp or the like made from the above as a single material, or to use two or more kinds thereof in combination.

In addition to the above pulp, various materials such as organic fibers such as acrylic fibers, rayon fibers, phenol fibers, polyamide fibers, polyester fibers, inorganic fibers such as glass fibers, carbon fibers, and alumina fibers are used as raw materials for forming bulky paper. It is also possible to mix the fibers. However, from the viewpoint of papermaking properties, it is preferable to add 50% by weight or more of natural wood pulp.

In the present invention, the density is 0.15 to 0.5.
The expandable particles used for the production of high-bulk paper having g / cm ³ are heat-expandable microcapsules having an expander made of a low boiling point liquid as a core and an outer shell made of a thermoplastic resin encapsulating the expander. Is used. This microcapsule contains isobutane, pentane, petroleum ether, hexane,
A volatile organic liquid (expanding agent) such as low boiling point halogenated hydrocarbons and methylsilane is wrapped in a thermoplastic resin shell made of a copolymer of vinylidene chloride, acrylonitrile, acrylic acid ester, methacrylic acid ester, etc. . When the microcapsules are heated above the softening point of the outer shell polymer, the outer shell polymer begins to soften, and at the same time, the vapor pressure of the encapsulating expander rises, the outer shell membrane is spread and the capsule expands.

The average particle size of the expandable particles before expansion is 10
Short-time heating at a relatively low temperature of 80 to 200 ° C. expands the diameter to about 4 to 5 times and the volume to 50 to 100 times to form closed cells. Therefore, a sheet obtained by mixing pulp and expandable particles and heat-foaming them contains a large number of bubbles and becomes a support having a low density and excellent heat insulation properties. When used as a support for an image-receiving sheet, the print density is improved. Let

In the present invention, the density is 0.15 to 0.5.
In order to obtain a bulky paper of g / cm ^3, the amount of the expandable particles to be added is 1 to 40 parts, preferably 3 to 20 parts, relative to 100 parts of pulp fiber, and the foaming temperature is 110 to 140 ° C. It is preferably within the range. If the content of expandable particles is less than 1 part, and if the heating temperature is less than 110 ° C, sufficient foaming cannot be obtained, and if it exceeds 40 parts, the effect is saturated and it is not economically feasible. become. When the foaming temperature is higher than 140 ° C., the outer shell of the microcapsule may melt and the closed cells may not be obtained.

In the present invention, 0.15 to 0.5 g / cm
^The papermaking pulp slurry used in the production of bulky paper having a density of ³ , in addition to pulp fibers and expandable particles, various retention aids conventionally used, paper strength enhancers,
One or more kinds of sizing agents and fillers can be mixed. Further, a papermaking slurry may be added with a papermaking additive such as a dye, a pH adjusting agent, a slime control agent, a defoaming agent, and a thickening agent, depending on the application. It is also possible to apply starch, polyvinyl alcohol, various surface sizing agents, pigments, etc. to the surface of the sheet before or after heat foaming by a size press or gate roll.

A sheet is made from a papermaking slurry containing the above-mentioned constituent raw materials as a main raw material by an ordinary papermaking machine. First, it is made into a sheet form through a wire part in the papermaking process, and then dehydrated by a press part. Next, a drying process is performed by the dryer part. The temperature of the surface of the multi-cylinder type or Yankee dryer of the dryer part causes the expandable particles mixed in the sheet to foam at the same time as the drying, and a large number of closed cells are formed in the sheet. It forms a body, which gives a foamed porous bulky paper having a low density and excellent heat insulation.

The high-bulk paper of the present invention has a basis weight of 10 to 100 g /
m ² is preferable, and more preferably 30 to 7
It is 0 g / m ² . If the basis weight is less than 10 g / m ² , a support having sufficient heat insulating properties may not be obtained, and if it exceeds 100 g / m ² , the load on the dryer of the paper machine becomes large and the economical efficiency deteriorates. Sometimes.

At least one coating layer is formed on one surface of the sheet-like support. The coating material for forming a coating layer is usually a coating material containing a binder resin as a main component and optionally a pigment. The coating material is applied onto the surface of the bulky paper to form at least one coating layer. Examples of the coating layer pigment include clay, kaolin, ground calcium carbonate, and rouxite clay in natural products, and light calcium carbonate, titanium oxide, aluminum hydroxide, plastic pigments and the like in synthetic products, which are used alone. Or, two or more kinds can be mixed and used.

The binder resin contained in the coating layer includes polyvinyl alcohol, oxidized starch, etherified starch, methoxycellulose, carboxymethylcellulose, hydroxyethylcellulose, casein, gelatin, soybean protein, polyvinylpyrrolidone, polyacrylamide and polyacrylic acid. Water-soluble resin such as styrene / butadiene copolymer latex (SB
R), copolymer latex such as metal methacrylate / butadiene copolymer latex, styrene-acrylic copolymer, acrylic ester copolymer, vinyl chloride-vinylidene chloride copolymer, emulsion of ethylene-vinyl acetate copolymer, etc. Is used. These resins are
Alternatively, two or more kinds can be mixed and used.

Since the image-receiving layer is formed on the coating layer by a solvent-based coating, it is excellent in film-forming ability and permeation of an organic solvent when it is important to develop the solvent barrier resistance. It is preferably formed of a water-soluble polymer capable of suppressing the above. Specifically, it is preferable to use polyvinyl alcohol, casein or the like. Further, pigments such as kaolin and calcium carbonate can be added within a range that does not impair the barrier property. The pigment used preferably has an average particle size of less than 2 μm. Other components of the coating layer include a dispersant, a water resistant agent, a water retention agent, a dye, and the like, and these are mixed and dispersed to obtain a coating layer coating material. The coating amount of the coating layer is preferably about 5 to 20 g / m ² per layer.

In the present invention, at least one coating layer is laminated, but it is desirable that at least one layer is a cast coating layer. When such a cast coating layer is used, bulky paper is used. It is possible to impart high smoothness to the surface of the.

The cast coating composition mainly comprises a mineral pigment and a binder resin, and is prepared by adding a coagulant, a release agent, a dye, etc., and dispersing and mixing. Pigments used,
As the resin, the same resin as the above-mentioned coating layer is used.
Casein is widely used as a resin, but since it is more expensive than other natural polymers such as starch and CMC, it is used in combination with SBR (latex) or S
It is being transformed to use BR alone. Further, it is one of the features that a release agent can be blended, but as the release agent, insoluble or soluble soaps such as magnesium oleate and ammonium stearate, animal and vegetable fats and oils, synthetic resins Emulsion, alkyl ketene dimer,
Examples include alkyl phosphates. The release agent is supplied to the surface of the cast drum to form a thin oil film to assist the peeling of the coating film, and the coating film carries out the oil film repeatedly.

As the coagulant, any coagulant such as an organic acid such as formic acid, croton, itaconic acid and acrylic acid, an electrolyte such as calcium formate and calcium chloride, which solidifies the adhesive component in the coating film can be used. . The above components are dispersed and mixed to obtain a cast paint. The mixing ratio is pigment:
Adhesive: Auxiliary agent = 100: 20: 5 is preferred.

This cast paint is applied in an amount of 15 to 30 g
Appropriately selected in the range of / m ² and coated on the base paper by various coating methods. That is, while the paint is still in a wet state, it is subjected to direct or slight drying treatment, and then it is pressed directly onto the mirror surface of the heated casting drum to dry it, or a semi-direct method, or a solidification effect after coating. A coating solution is brought into contact with an aqueous solution (such as an aqueous solution of an acid or an electrolyte) to gelate it, and then it is pressed onto a cast drum to dry it, or a coagulation method in which it is dried. A coating layer having high surface smoothness is formed by a cast coating method such as a rewetting method in which an aqueous solution of a wetting agent or the like is applied to swell the coating film surface and press-bonded to a cast drum.

In the thermal transfer receiving sheet of the present invention, the image receiving layer provided on the coating layer is mainly composed of a dye receiving resin capable of dyeing the sublimable dye transferred from the ink ribbon. Examples of such dyeing resin include polyester resin, polycarbonate resin, vinyl chloride-vinyl acetate copolymer resin, acrylic resin, cellulose derivative, and resin cured by irradiation with active energy rays.

A resin crosslinking agent, a lubricant, a release agent, a pigment, etc. are usually added to the image-receiving layer as necessary for the purpose of preventing fusion with the ink sheet due to heat during printing. . Further, other additives such as pigments, fluorescent dyes, dyes such as blue and violet, ultraviolet absorbers, antioxidants and the like can be added as required. These additives may be mixed and applied with the main component of the image receiving layer, or may be provided as a separate coating layer above or below the image receiving layer.

In addition, a layer containing an antistatic agent may be provided on at least one surface of the image receiving sheet in order to prevent running troubles due to static electricity generated while the image receiving sheet is running in the printer. A cationic hydrophilic polymer material is advantageously used as the antistatic agent.

The image-receiving layer and other coating layers of the image-receiving sheet of the present invention are coated with a coater such as a bar coater, a gravure coater, a blade coater, an air knife coater, a comma coater and a gate roll coater, and dried. It is formed.

The thickness of the image receiving layer of the image receiving sheet of the present invention is preferably 1 to 10 μm, more preferably 2 to 6 μm. When the thickness of the image receiving layer is less than 1 μm, the density and sensitivity of the image may be reduced, or the gloss of the printed surface may be reduced. If it is thicker than 10 μm, the effect is saturated, which is uneconomical and the strength of the image receiving layer may be lowered.

[0033]

The present invention will be explained in more detail by the following examples, but the scope of the present invention is not limited by these examples. In each example, "%" indicates% by weight and "part" indicates part by weight.

Example 1 80% hardwood bleached pulp (LBKP) beaten to 450 ml Canadian standard freeness (CSF) and Canadian standard freeness (C)
SF) Bleached softwood pulp (NBKP) beaten to 470 ml
Into a pulp slurry in which a pulp composed of 20% is dispersed, expandable microcapsule particles (Matsumoto Yushi-Seiyaku Co., Ltd., trade name: Matsumoto Microsphere F-30D, particle diameter 1
0-20 μm, maximum foaming temperature 130 ° C) 5%, dry paper strength enhancer (trade name: Polystron 117, manufactured by Arakawa Chemical Industry Co., Ltd.)
0.2%, cationized starch (Oji National, trademark:
CATO-15) 1.0%, alkyl ketene dimer sizing agent (trade name: size pine K90, manufactured by Arakawa Chemical Industry Co., Ltd.)
3) 0.03% and 0.4% of a wet paper strength enhancer (trade name: Kamen 557H, manufactured by DIC Hercules) are added with good stirring, and the pH of the obtained papermaking slurry is 7.
Was adjusted to 3, and the pulp concentration was adjusted to 0.03%.

Using the papermaking slurry thus obtained, papermaking is carried out by means of an inclined net paper machine, and the sheet formed is subjected to a surface temperature of 130.
After drying with a Yankee dryer at ℃ to foam the expandable particles and drying with a multi-cylinder dryer, machine calendering at a linear pressure of 30 kg / cm, basis weight 60 g / m ² , thickness 120
A high-bulk paper having a micrometer and a density of 0.5 g / cm ³ was prepared.

On the surface of this bulky paper, polyvinyl alcohol as an organic solvent resistant polymer was applied at a dry coating amount of 5.0 g / m ² to form a coating layer.

An image-receiving sheet was prepared by coating the above-obtained sheet with a composition for forming an image-receiving layer having the following composition so that the thickness after drying was 10 μm, and drying to form an image-receiving layer. . Image-Receptive Layer-Forming Composition Component Weight Parts Polyester Resin 100 Parts (Toyobo, Trademark: Byron 200) Silicon Oil 3 Parts (Shin-Etsu Silicon, Trademark: KF393) Isocyanate 5 Parts (Takeda Yakuhin, Trademark: Takenate D-110N) ) Toluene 300 parts

Example 2 An image receiving sheet was prepared by the same steps as in Example 1. However, when forming the coating layer, a coating clay (trademark: Ansilex 9) is used instead of the coating material for the coating layer containing the organic solvent resistant polymer.
3) 75%, calcium carbonate (trademark: Softon 220)
0, Shiraishi calcium 20%, titanium dioxide (trademark:
W-10, manufactured by Ishihara Sangyo) 5%, and sodium pyrophosphate 0.5% were mixed and stirred in a kneader with 35% of water, and a 15% concentration casein solution 13 separately dissolved therein was added.
% (Dissolved with stirring at 60 ± 1 ° C. for 0.5 hours in the presence of 1.5% caustic soda based on pure casein),
Next, after mixing 17% of styrene butadiene copolymer latex (as solid content) and thoroughly stirring, 0.25% of ammonium oleate was added to this so that the solid content concentration of the paint was finally 40%. Using the adjusted paint,
A cast coat layer was formed on the foamed high-bulk paper described above so that the dry weight was 25 g / m ² , to form a coating layer.

Example 3 An image receiving sheet was produced by the same steps as in Example 1. However, in forming the coating layer, 69% of calcium carbonate, 11% of modified starch and various auxiliary agents are mixed and stirred in Cowles,
To this, 8% of styrene butadiene copolymerized latex and 0.08% of wetting agent were added and stirred sufficiently to make the solid content of the coating 4
A coating adjusted to 0% was applied on one surface of the sheet-shaped support by a metering bar system at a coating amount of 13 g / m ² to form a coating layer, and further, organic resistance 5.0 consisting of polyvinyl alcohol as the solvent polymer
A layer of g / m ² was formed by coating.

Example 4 An image receiving sheet was prepared in the same manner as in Example 1. However, when forming the coating layer, the same coating layer as in Example 3 was applied,
A cast coat layer similar to that of Example 2 was formed thereon.

Example 5 An image-receiving sheet was prepared in the same manner as in Example 1. However, when forming the coating layer, a cast coat layer similar to that in Example 2 was formed, and a polyvinyl alcohol layer similar to Example 1 was formed thereon.

Example 6 An image receiving sheet was prepared in the same manner as in Example 1. However, when forming the coating layer, the same coating layer as in Example 3 was applied,
After applying the cast coating material, a cast coat layer similar to that in Example 2 was formed, and a polyvinyl alcohol layer similar to Example 1 was formed thereon.

Comparative Example 1 An image receiving sheet was prepared in the same manner as in Example 3. However, the sheet support has a basis weight of 91 g / m ² and a thickness of 120 μm.
m, density 0.76 g / cm ³ of high quality paper was used.

Performance Test Each of the image-receiving sheets obtained in each of Examples 1 to 6 and Comparative Example 1 was provided with a color bar signal generator (Shibazoku, trademark: C).
13A2) was printed with a thermal transfer printer (trade name: UP5000, manufactured by Sony), and the obtained print image was evaluated for density and unevenness in density of the printed image. The results are shown in Table 1.

Each evaluation was carried out as follows. 1. Print Density The maximum density of the printed image is the Macbeth densitometer (RD-91
4, manufactured by Kollmorgen Corp.). 2. Density unevenness Based on a receiving sheet using a laminated base material of synthetic paper / coated paper / synthetic paper, the density unevenness of the printed image is 3 for good, 2 for general quality, and 2 for inferior. Sensory evaluation was performed in three stages as 1.

[0046]

[Table 1]

[0047]

In the (sublimation type) thermal transfer image-receiving sheet of the present invention, the sheet-shaped support has a density of 0.15 to 0.5 g / cm 3.
By forming at least one or more coating layers including cast coat processing on one surface of the bulky paper of ³ , it is possible to obtain prints with high print density and excellent image quality, which is of practical value. It is expensive.

Claims (2)

[Claims] 1. A sheet-shaped support, at least one coating layer formed on one surface of the sheet-shaped support and containing a resin as a main component, and a thermal transfer image formed on the coating layer. Receiving a forming dye, having an image receiving layer for dyeing, the sheet-shaped support is obtained by making a papermaking slurry containing pulp and expandable particles, and foaming the obtained base paper by heating. And 0.15 to 0.5 g / cm ³
A thermal transfer image-receiving sheet, which is a bulky paper having a density of 1. 2. At least one of the coating layers is formed by cast coating in which a coating layer formed of a coating liquid composition containing a pigment and a resin as a main component is pressed against a heating drum surface to give a gloss finish. The thermal transfer receiving sheet according to claim 1, which is