JP2011037246A - Thermal transfer recording medium and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal transfer recording medium that hardly cause a color cast in a low gradation section, has a gradation property to achieve a high density, and has high image uniformity. <P>SOLUTION: The thermal transfer recording medium includes: a paper base material 11; resin layers 12 and 13 which cover both sides of the paper base material 11; two or more coating layers 17 formed on one side of the paper base material 11 through the resin layer 12. The coating layer 17 has a hollow layer 14 where a layer that is the nearest to the paper base material 11 contains void and an image receiving layer 16 that contains a polymer compound in which an outermost layer that is the furthest from the paper base material 11 has the lower limit critical temperature. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a thermal transfer recording medium and a manufacturing method thereof.

Conventionally, a so-called dye thermal transfer system is known as an image forming technique for a color image or a monochrome image. In this method, an ink sheet containing a heat diffusible dye having a property of diffusing and transferring by heating is opposed to the dye receiving layer of the image receiving sheet, and the heat diffusing dye is applied to the dye receiving layer using a thermal head. Is an image-like transfer technology.
The thermal transfer method is well-established as a method that enables image formation using digital data, does not use a processing solution such as a developer, and can produce a gradation expression comparable to a silver salt photograph.

On the other hand, an attempt has been made to adjust the thermal properties of the polymer compound used in the receiving layer in order to efficiently transfer the dye with respect to the energy from the same thermal head (see, for example, Patent Document 1). ).
That is, an attempt to achieve a high printing density by using resin fine particles having a glass transition point adjusted to 50 ° C. to 120 ° C. as a dye receiving layer has been reported. According to this method, it is possible to improve the printing density at the time of high energy printing, but the so-called color fog phenomenon, in which color development exceeding the required density occurs in accordance with printing at low energy, is remarkable. Therefore, it has been difficult to achieve both sufficient gradation characteristics and printing density.

  A hollow layer or a barrier layer containing a polymer compound having a lower critical temperature is applied on the cellulose pulp base material. Thereafter, a method for forcibly cooling the system and utilizing the temperature-sensitive thickening effect of a polymer compound having a lower critical temperature to achieve image uniformity and high density has been reported (for example, patents According to this method, since the coating layer is provided on the water-absorbing cellulose pulp base material, the coating liquid is absorbed by the cellulose pulp base material. Even if the film surface direction is inferior in uniformity and the sensitivity is sufficient, it cannot be said that a sufficient effect is obtained from the viewpoint of image uniformity.

Japanese Patent Application Laid-Open No. 06-13517 JP 2005-335174 A JP 2008-302529 A

  The problems to be solved are that a high printing density is achieved at the time of high energy printing, but the color fog phenomenon at the time of low energy printing becomes remarkable, and a polymer compound having a lower critical temperature is coated on the cellulose pulp base material. Even if it is processed, the image uniformity cannot be sufficiently obtained.

  The present invention enables a thermal transfer recording medium with low color gradation in the low gradation portion, good gradation that can achieve a high density, and high image uniformity.

  The thermal transfer recording medium of the present invention includes a paper base material, a resin layer covering both sides of the paper base material, and a plurality of coating layers formed on one surface of the paper base material via the resin layer The plurality of coating layers include a polymer compound in which the layer closest to the paper substrate is a hollow layer including voids, and the outermost layer farthest from the paper substrate has a lower critical temperature. It consists of an image receiving layer.

In the thermal transfer recording medium of the present invention, the outermost surface layer farthest from the paper substrate is composed of an image receiving layer containing a polymer compound having a lower critical temperature. Such a polymer compound has a property of changing the responsiveness to heat depending on the temperature and humidity of the system. For this reason, in printing with a thermal head below the lower critical point temperature, the polymer chains are dehydrated and self-aggregated, so that the dye transferred from the ink ribbon is difficult to diffuse.
On the other hand, in printing with the energy of the thermal head above the lower critical point temperature, the polymer chain in the dried coating film is spread by thermal motion, the apparent polymer softening point is lowered, and the dye is likely to diffuse. .
That is, in the low gradation area printing with low energy, the gradation becomes gentle with respect to the applied energy, so that an image without so-called “fogging” is obtained, and a high density can be obtained in the high gradation area.
In addition, since the outermost layer of the plurality of coating layers is composed of a layer containing a polymer compound having a lower critical temperature, after coating the outermost layer coating liquid at the lower critical temperature or higher, the coating film is moved to the lower critical temperature or lower. By lowering the temperature, thickening or gelation mediated by hydrophobic interaction occurs. As a result, a uniform film surface free from blown roughening by dry air can be obtained.

The method for producing a thermal transfer recording medium of the present invention comprises a step of forming a thermal transfer recording medium by applying a plurality of coating layers on a paper substrate whose both surfaces are covered with a resin layer, and then drying the thermal transfer recording medium. A step of winding the recording medium, wherein the plurality of coating layers are formed of a hollow layer in which the coating layer closest to the paper substrate includes voids, and the coating of the outermost layer farthest from the paper substrate The working layer is formed of an image receiving layer containing a polymer compound having a lower critical temperature, and the water content of the thermal transfer recording medium is adjusted to ² g / m ² to 10 g / m ² and wound.

In the method for producing a thermal transfer recording medium of the present invention, the outermost image-receiving layer farthest from the paper substrate is formed of a layer containing a polymer compound having a lower critical temperature. For this reason, in printing with a thermal head below the lower critical point temperature, the polymer chains are dehydrated and self-aggregate, so that the dye transferred from the ink ribbon becomes difficult to diffuse.
On the other hand, in printing with the energy of the thermal head above the lower critical point temperature, the polymer chains in the dried coating film are spread by thermal motion, the apparent polymer softening point is lowered, and the dye is likely to diffuse.
That is, in the low gradation area printing with low energy, the gradation becomes gentle with respect to the applied energy, so that an image without so-called “fogging” is obtained, and a high density can be obtained in the high gradation area.
Further, since the outermost image-receiving layer of the plurality of coating layers is composed of a layer containing a polymer compound having a lower critical temperature, the lowermost critical temperature is applied after coating the outermost layer coating liquid at the lower critical temperature or higher. In the following, by lowering the temperature of the coating film, viscosity increase or gelation is caused by hydrophobic interaction. As a result, a uniform film surface free from blown roughening by dry air can be obtained.
Furthermore, since the water content of the thermal transfer recording medium is adjusted to ² g / m ² or more and 10 g / m ² or less, the above-mentioned effect is easily exhibited, and the outermost layer and substrate of the thermal transfer recording medium wound up by a roll Adhesion is prevented between the back surfaces.
On the other hand, if the water content of the thermal transfer recording medium is less than 2 g / m ² , the response of the polymer compound at the lower critical temperature is not sufficient, and the effects of the present invention cannot be obtained sufficiently. If the water content is greater than 10 g / m ² , adhesion occurs between the outermost layer wound on the roll and the back surface of the substrate. A so-called “blocking” phenomenon occurs.

  The thermal transfer recording medium of the present invention makes it possible to provide a thermal transfer recording medium with low color gradation in the low gradation portion, good gradation that can achieve a high density, and high image uniformity. .

  The method for producing a thermal transfer recording medium of the present invention is to produce a thermal transfer recording medium with low color gradation in a low gradation portion, good gradation that can achieve a high density, and high image uniformity. enable.

1 is a schematic cross-sectional view showing an example of the configuration of a thermal transfer recording medium according to a first embodiment of the present invention. It is explanatory drawing at the time of the coating of the high molecular compound which has a minimum critical temperature. It is explanatory drawing at the time of the printing of the high molecular compound which has a minimum critical temperature.

  Hereinafter, modes for carrying out the invention (hereinafter referred to as embodiments) will be described.

<1. First Embodiment>
[Example of thermal transfer recording medium]
An example of the configuration of the thermal transfer recording medium according to the first embodiment of the present invention will be described with reference to the schematic sectional view of FIG.

[Basic structure of thermal transfer recording medium]
As shown in FIG. 1, the thermal transfer recording medium 1 has a hollow layer 14 on one surface on a paper substrate 11 covered on both sides with a resin layer 12 and a resin layer 13, for example, via the resin layer 12. In this configuration, a plurality of coating layers 17 including the barrier layer 15 and the image receiving layer 16 are formed in this order.
The image receiving layer 16 is a receiving layer made of a resin having dye receiving ability, and is a layer containing a polymer compound having a lower critical temperature.
The hollow layer 14 is made of a resin layer having at least voids in the membrane.
The barrier layer 15 is made only of resin, and there is no void.

[Polymer compound having lower critical temperature]
The polymer compound having the lower critical temperature in the image receiving layer 16 refers to a polymer compound having both a hydrophilic part and a hydrophobic part in the molecule, and reversibly changes the balance between hydrophilic and hydrophobic. It is a high molecular compound.
Such a polymer includes poly N-substituted acrylamide. Examples of the poly N-substituted acrylamide include polyisopropyl acrylamide, hydrophobized pullulan, modified polyethylene oxide, amphiphilic star polymer described in JP-A No. 2002-146256, JP-A No. 11-322866, There are compounds selected from poly-modified vinyl, poly-modified vinyl ether compounds and the like described in each publication such as Kaihei 11-322742, JP-A 2000-319473, and JP-A 2001-19770. The form may be a linear polymer or a star polymer emulsion having a polymer nucleus. In particular, a star-shaped polymer emulsion having a polymer nucleus is preferable from the viewpoint of handling properties.

In the above compound group, the monomer is particularly preferably an N-substituted acrylamide compound or a vinyl ether compound.
Specific examples of the compound include N-substituted (meth) acrylamide derivatives and vinyl methyl ether derivatives. Among them, preferred monomers for obtaining the effects of the present invention include N-substituted (meth) acrylamide derivatives, and N-ethylmethacrylamide, Nn-propylacrylamide, N-isopropylacrylamide, N -Isopropylmethacrylamide, N-cyclopropylacrylamide, N-cyclopropylmethacrylamide, N, N-diethylmethacrylamide, N-methyl-N-isopropylacrylamide, N-methyl-Nn-propylacrylamide, N-ethoxyethyl Examples include acrylamide, N, N′-bis (methoxyethylacrylamide), 3-dimethyl (methacryloyloxyethylammonium propanesulfonate), and the like. Among them, N-isopropylacrylamide is particularly preferable.

In the present invention, it is more preferable that the amphiphilic substance has a core-shell structure. For example, a core shell having a core portion made of a (meth) acrylic polymer and an outer shell portion made of an N-alkylacrylamide polymer described in JP-A-7-33224, JP-A-2003-40916, and the like Examples thereof include polymer fine particles having a structure.
Such a polymer compound has a property of changing the responsiveness to heat depending on the temperature and humidity of the system. Therefore, when printing with a thermal head at a low energy below the lower critical temperature, as shown in FIG. 2 (1), the polymer chain is dehydrated and self-aggregates, so that the dye transferred from the ink ribbon diffuses. It is difficult to do.

On the other hand, as shown in Fig. 2 (2), when printing with a thermal head at a high energy above the lower critical temperature, the polymer chain in the dried coating is in a state of spreading due to thermal motion, and apparent polymer softening The spots go down and the dye is more likely to diffuse.
That is, in the low gradation area printing with low energy, the gradation becomes gentle with respect to the applied energy, so that an image without so-called “fogging” is obtained, and a high density can be obtained in the high gradation area.

The above phenomenon appears as a remarkable effect when moisture in the paper substrate 11 or in the atmosphere coexists, and it is preferable to adjust the water content in the paper substrate 11 at the time of production to obtain the effect of the present invention. In order to obtain this preferred embodiment, it is preferable to adjust the water content of the thermal transfer recording medium (paper) to 2g / m ² ~25g / m ² when winding the thermal transfer recording medium (printing paper) during manufacture.
In addition, as shown in FIG. 3 (1), at the time of production, the outermost layer coating liquid is applied at a temperature not lower than the lower critical temperature (for example, coating liquid temperature 40 ° C.). At this time, the polymer chain is in a contracted state. Thereafter, as shown in FIG. 3 (2), by lowering the temperature of the coating film below the lower critical temperature (for example, coating liquid temperature 15 ° C.), the polymer chain spreads, and the coating liquid on the outermost coating layer becomes It causes thickening or gelation (expression of low temperature setting property) mediated by hydrophobic interaction. As a result, a uniform film surface free from blown rough by the dry air can be obtained.
In order to achieve the above, it is preferable to adjust the viscosity of the coating solution before coating to 30 ° C. or more and 45 ° C. or less and to cool the whole including the support to 15 ° C. or less after coating.
Thereafter, as shown in FIG. 3 (3), when the coating solution is dried, the polymer chain contracts.

[Image receiving layer]
For the image receiving layer 16 of the thermal transfer recording medium 1, it is preferable to use a resin that is easily dyed.
Specifically, polyolefin resins such as polypropylene, halogenated resins such as polyvinyl chloride and polyvinylidene chloride, vinyl resins such as polyvinyl acetate, polyacrylate, polyvinyl butyral, and polyvinyl acetal, hydroxyethyl acrylate, phenyl Copolymers of acrylates such as methyl methacrylate, polyester resins such as polyethylene terephthalate and polybutylene terephthalate, polystyrene resins such as polystyrene and polystyrene acrylonitrile, polyamide resins, phenoxy resins, olefins such as ethylene and propylene, and other vinyl monomers Using polymers, polyurethanes, polycarbonates, acrylic resins, ionomers, cellulose derivatives, etc., and copolymers, or mixtures thereof It is possible. Among these, acrylic resins, derivatives and copolymers are preferable.

The image receiving layer 16 is composed of, for example, a heat diffusible dye receiving layer, and it is preferable to add a release agent to the layer for the purpose of preventing heat fusion with the heat diffusible dye receiving layer.
As the mold release agent, a phosphoric ester plasticizer, a fluorine compound, silicone oil (including reaction curable silicone) and the like can be used, and silicone oil is more preferable. Various modified silicones including dimethyl silicone can be used for the silicone oil. Specifically, amino-modified silicone, epoxy-modified silicone, alcohol-modified silicone, vinyl-modified silicone, urethane-modified silicone and the like are used. These silicones can also be blended or polymerized using various reactions.
One type of release agent may be used, or two or more types of release agents may be used in combination.
The amount of the release agent added is preferably 0.5 to 30 parts by mass with respect to 100 parts by mass of the binder resin used for the image receiving layer 16. When the range of the addition amount is not satisfied, problems such as fusion between the thermal transfer sheet and the image receiving layer 16 of the thermal transfer recording medium 1 or a decrease in printing sensitivity may occur. Note that these release agents may be provided as a separate release layer on the image receiving layer 16 without being added to the image receiving layer 16.

[Paper base coated with resin layers on both sides]
In order to obtain a high-quality image with a recorded image close to photographic quality and at a low cost, it is particularly preferable to use a laminated paper in which both sides of the paper substrate 11 are laminated with a resin layer 12 (for example, polyethylene). The laminated paper laminated with such polyethylene will be described below.

The paper base 11 (base paper) used for the laminated paper can be obtained by making paper using wood pulp as a main raw material and adding synthetic pulp such as polypropylene or synthetic fiber such as nylon or polyester as necessary. As wood pulp, any of LBKP, LBSP, NBKP, NBSP, LDP, NDP, LUKP, and NUKP can be used, but it is preferable to use more LBKP, NBSP, LBSP, NDP, and LDP with a large amount of short fibers. However, the ratio of LBSP to LDP is preferably 10% by weight or more and 70% by weight or less.
The pulp is preferably a chemical pulp with few impurities (sulfate pulp, sulfite pulp, etc.), and a pulp that has been whitened by bleaching is also useful.

In the base paper, sizing agents such as higher fatty acids and alkyl ketene dimers, white pigments such as calcium carbonate, talc and titanium oxide, paper strength enhancing agents such as starch, polyacrylamide and polyvinyl alcohol, fluorescent whitening agents, polyethylene glycols A water retaining agent such as a dispersant, a softening agent such as a quaternary ammonium, and the like can be appropriately added.
The freeness of pulp used for papermaking is preferably 200 cc to 500 cc as defined by CSF, and the fiber length after beating is 24 mesh residual weight% and 42 mesh residual weight% specified in JIS-P-8207. Is preferably 30% to 70%. In addition, it is preferable that 4 mesh remainder weight% is 20 weight% or less.
The basis weight of the base paper is preferably 30 g to 250 g, particularly preferably 100 g to 200 g. The thickness of the base paper is preferably 120 μm to 250 μm.
The base paper can be given high smoothness by calendering at the paper making stage or after paper making. The density of the base paper is generally 0.7 g / m ^{2 to} 1.2 g / m ² (JIS-P-8118). Furthermore, the base paper stiffness is preferably 20 to 200 g under the conditions specified in JIS-P-8143.

A surface sizing agent may be applied to the surface of the base paper. As the surface sizing agent, a sizing agent similar to the size that can be added to the base paper can be used.
The pH of the base paper is preferably 5 to 9 when measured by the hot water extraction method defined in JIS-P-8113.

As the polyethylene of the resin layers 12 and 13 covering the front and back surfaces of the paper base 11 (base paper), either one or both of low density polyethylene (LDPE) and high density polyethylene (HDPE) is mainly used. Moreover, a part of linear low density polyethylene (LLDPE), polypropylene, etc. can also be used.
In particular, as the polyethylene layer on the image receiving layer 16 side, rutile-type titanium oxide or anatase-type titanium oxide is added to polyethylene as widely used in photographic paper, and the opacity and whiteness are improved. Is preferably used. The titanium oxide content is generally 3% to 20% by weight, preferably 4% to 13% by weight, based on polyethylene.
Polyethylene-coated paper can be used as glossy paper. Also, when polyethylene is melt-extruded and coated on the surface of the base paper, a so-called molding process is performed to give the same matte surface and silk texture as in ordinary photographic printing paper. A surface may be formed.
In the polyethylene-coated paper, it is particularly preferable to keep the water content in the paper at 3 wt% to 10 wt%.

[Hollow layer to hollow particle]
A hollow layer 14 is preferably provided in the layer structure of the thermal transfer recording medium 1. The hollow layer 14 is formed by forming a layer using hollow particles having voids (for example, pores) in the particles themselves, using voids (for example, gaps) formed between the particles, or having both of them. Even if it exists, it can use preferably.

The hollow polymer used for the hollow layer 14 is polymer particles having independent voids (for example, pores) inside the particles. Such polymer particles include, for example,
(1) Non-foaming type in which water is contained in the partition walls formed of polystyrene, acrylic resin, styrene-acrylic resin, etc., and after coating and drying, the water in the particles evaporates outside the particles and the inside of the particles becomes hollow There are hollow particles.
(2) Foamed micro that is covered with a low-boiling liquid such as butane or pentane with a resin comprising any of polyvinylidene chloride, polyacrylonitrile, polyacrylic acid, polyacrylic acid ester, a mixture thereof, or a polymer. There is a balloon. This foaming type microballoon becomes hollow when the low boiling point liquid inside the particles expands by heating after coating.
(3) There is a microballoon in which the above (2) is preheated and foamed into a hollow polymer.
These hollow polymers preferably have a hollow ratio of about 20% to 70%, and can be used as a mixture of two or more if necessary.

Specific examples of the above (1) include, for example, Ropaque 1055 manufactured by Law and Haas, Lowpaque Ultra E, EPX-3831, EPX3841, Boncoat PP-1000 manufactured by Dainippon Ink, SX866 (B) manufactured by JSR, Japan Examples include Nippon MH5055, MH8101, and MH8055 (all trade names) manufactured by Zeon.
Specific examples of (2) include F-30 and F-50 (both trade names) manufactured by Matsumoto Yushi Seiyaku Co., Ltd.
Specific examples of the above (3) include, for example, F-30E manufactured by Matsumoto Yushi Seiyaku Co., Ltd., EXPANSEL 461DE, 551DE, 551DE20 (all trade names) manufactured by Nippon Ferrite Co., Ltd.

  The hollow layer 14 containing the hollow polymer contains a crosslinked hydrophilic binder such as a water-dispersed resin or a water-soluble resin as a binder resin. The binder resin used in the hollow layer 14 includes acrylic resin, styrene-acrylic copolymer, polystyrene resin, polyvinyl alcohol resin, vinyl acetate resin, ethylene-vinyl acetate copolymer, vinyl chloride vinyl acetate copolymer, Resins such as styrene-butadiene copolymer, polyvinylidene chloride resin, cellulose derivatives, casein, starch, and gelatin can be used. These resins can be used alone or in combination.

The solid content of the hollow polymer in the hollow layer 14 is preferably between 5 parts by mass and 2000 parts by mass when the solid content of the binder resin is 100 parts by mass. Moreover, 1 mass%-70 mass% are preferable, and, as for the mass ratio which occupies with respect to the coating liquid of the solid content of a hollow polymer, 10 mass%-40 mass% are more preferable. If the ratio of the hollow polymer is too small, sufficient heat insulation cannot be obtained, and if the ratio of the hollow polymer is too large, the binding force between the hollow polymers decreases, causing problems such as powder falling off during processing or film peeling. Arise.
The particle size of the hollow polymer is preferably 0.1 μm to 20 μm, more preferably 0.1 μm to 2 μm, and particularly preferably 0.1 μm to 1 μm. Further, the glass transition temperature (Tg) of the hollow polymer is preferably 70 ° C. or higher, and more preferably 100 ° C. or higher.

[Barrier layer]
Between the hollow layer 14 including voids (for example, pores, gaps, etc.) and the outermost image-receiving layer 16 of the plurality of coating layers 17, a barrier composed of a resin layer made only of a resin having no voids It is preferable to provide the layer 15.
Any resin can be used as the resin used for the barrier layer 15 as long as it does not have voids in the resin. For example, it is made of a polyvinyl alcohol resin.

<2. Second Embodiment>
[Example of manufacturing method of thermal transfer recording medium]
An example of a method for manufacturing a thermal transfer recording medium according to the first embodiment of the present invention will be described with reference to the schematic cross-sectional view of FIG.

In the manufacturing method of the thermal transfer recording medium 1, the thermal transfer recording medium 1 is formed by applying a coating layer 17 composed of a plurality of layers on the paper base 11 covered on both sides with the resin layers 12 and 13 and then drying. .
The coating layer 17 is obtained by, for example, coating the hollow layer 14, the barrier layer 15, and the image receiving layer 16 in this order from the resin layer 12 side and drying.
The thermal transfer recording medium 1 thus formed is wound up, for example, on a roll.
The water content of the thermal transfer recording medium 1 when the thermal transfer recording medium 1 is wound on a roll is adjusted to ² g / m ^{2 to} 25 g / m ² .

[Coating process]
The coating layer 17 can be appropriately selected from methods such as roll coating, bar coating, gravure coating, gravure reverse coating, die coating, slide coating, and curtain coating. Among these, curtain coating and slide coating can be applied simultaneously to each layer, and are preferred forms when at least two or more layers are applied. The coating speed is preferably 50 m / m or more and 600 m / min or less, and the viscosity of each layer of the coating liquid is preferably 10 cp or more and 300 cp or less. It is also preferable to adjust the surface tension using a surfactant for each layer.

[Drying process]
The drying process is a constant rate drying period in which the evaporation of water from the coating film surface is rate-limiting and the coating film temperature is substantially equal to the wet bulb temperature, and the movement of water in the coating film is rate-limiting and the coating film temperature is higher than the wet bulb temperature. Drying progresses through an increasing rate of drying. In order to obtain a good film surface, it is preferable that the film surface temperature during the decreasing rate drying period is lower than the film surface temperature during the constant rate drying period.

[Winding process]
It is preferable to adjust the water content to 2 g / m ² or more and 10 g / m ² or less by humidifying or adjusting the dry water content when winding on the roll after the end point of drying.
When the water content of the thermal transfer recording medium 1 is less than 2 g / m ² , the response of the polymer compound at the lower critical temperature is not sufficient, and the effects of the present invention may not be sufficiently obtained. If the water content is greater than 10 g / m ² , adhesion occurs between the outermost layer wound on the roll and the back surface of the substrate. This is not preferable because a so-called “blocking” phenomenon or thermal fusion with the ink ribbon may occur at the time of printing, particularly at high density printing that requires high energy.

<Example>
Hereinafter, specific examples to which the present invention is applied will be described in detail based on experimental results.

[Synthesis of polymer materials with lower critical temperature]
[Preparation of polymer fine particle 1]
Monomer liquid 1 was prepared by mixing 75 parts of phenylmethyl methacrylate, 20 parts of 2-hydroxyethyl acrylate, and 2 parts of ethylene glycol dimethacrylate.
To a four-necked flask, 0.2 part of dodecyl sulfate and 180 parts of ion-exchanged water were added and dissolved, and then purged with nitrogen. In this, 5 parts of monomer liquid 1 was added, and it heated up at 60 degreeC, stirring. After the temperature rise, 3 parts of 2% ammonium persulfate aqueous solution was dropped, and the temperature was further raised to 80 ° C., and the remaining 25.5 parts of monomer liquid 1 and 40 parts of 2% ammonium persulfate aqueous solution were dropped over 3 hours. And aged for 2 hours to prepare a core part.
While maintaining the above reaction solution at 80 ° C., a mixed solution of 100 parts of N-isopropylacrylamide and 1000 parts of ion-exchanged water and 240 parts of 0.2% ammonium persulfate were dropped over 2 hours and aged for 4 hours. did. Thereafter, centrifugal separation was performed to remove coarse particles, and an aqueous dispersion containing polymer compound fine particles (polymer fine particles 1) having a core-shell structure with an average particle size of 148 nm was prepared. The average particle diameter was measured using, for example, a Zetasizer 1000HS manufactured by Malvern.
Hereinafter, the fine particles in Examples refer to those having an average particle diameter of 3 μm or less, for example.

[Preparation of polymer fine particle 2]
In the preparation of the polymer fine particle 1, 0.2 part of C ₁₂ H ₂₅ O (CH ₂ CH ₂ O) ₉ H was used instead of 0.2 part of dodecyl sulfate, and 2- An aqueous dispersion containing a viscosity-inhibiting substance (polymer fine particles) 2 having a core-shell structure with an average particle size of 220 nm was obtained in the same manner except that ethoxyethyl vinyl ether was used.

[Adjustment of polymer fine particle 3]
10% polymer fine particles 3 were obtained in the same manner as in the preparation of the polymer fine particles 1 except that 400 parts of water was added without adding N-isopropylacrylamide and ammonium persulfate.

[Preparation of polymer compound 1]
A monomer liquid 2 was prepared by mixing 25 parts of phenylmethyl methacrylate, 30 parts of butyl acrylate, 25 parts of 2-hydroxyethyl acrylate, and 20 parts of N-isopropylacrylamide.
After adding 100 parts of methyl ethyl ketone and 10 parts of monomer liquid 2 to the four-necked flask, the atmosphere was replaced with nitrogen. After raising the temperature to 60 ° C. with stirring, 2 parts of benzoyl peroxide and 100 parts of monomer liquid 2 were added over 2 hours to obtain polymer compound 1.

[Preparation of polymer compound 2]
Monomer liquid 3 was prepared by mixing 50 parts of phenylmethyl methacrylate, 5 parts of butyl acrylate, and 15 parts of hydroxyethyl acrylate.
After adding 100 parts of methyl ethyl ketone and 10 parts of monomer liquid 3 to the four-necked flask, the atmosphere was replaced with nitrogen. After heating to 60 ° C. with stirring, 1.5 parts of benzoyl peroxide and 80 parts of monomer solution 3 were added over 2 hours, and then 0.5 part of benzoyl peroxide and 20 parts of N-isopropylacrylamide were added for 1 hour. The polymer compound 2 was obtained.

[Preparation of polymer compound 3]
Monomer liquid 3 was prepared by mixing 50 parts of phenylmethyl methacrylate, 5 parts of butyl acrylate, and 15 parts of hydroxyethyl acrylate.
After adding 100 parts of methyl ethyl ketone and 10 parts of monomer liquid 3 to the four-necked flask, the atmosphere was replaced with nitrogen. After raising the temperature to 60 ° C. with stirring, 1.5 parts of benzoyl peroxide and 80 parts of monomer liquid 3 were added over 2 hours to obtain polymer compound 3.

[Preparation of receiving layer coating solution]
[Preparation of Receptive Layer Coating Liquid 1]
To 20 parts of the 10% polymer fine particle 1 dispersion, 0.4 part of basic processed gelatin (for example, type SR manufactured by Nitta Gelatin Co., Ltd.) is added and dissolved by heating to 40 ° C. A working liquid 1 was obtained.

[Preparation of Receptive Layer Coating Liquid 2]
A receiving layer coating solution 2 was obtained in the same manner except that the dispersion of polymer fine particles 2 was used instead of the dispersion of polymer fine particles 1.

[Preparation of Receptive Layer Coating Liquid 3]
A receiving layer coating solution 3 was obtained in the same manner except that the dispersion of polymer fine particles 3 was used instead of the dispersion of polymer fine particles 1.

[Preparation of Receptive Layer Coating Liquid 4]
A receiving layer coating solution 4 was obtained in the same manner except that a vinyl chloride latex (for example, vinylfuran 900 manufactured by Nissin Chemical Industry Co., Ltd.) was used instead of the dispersion of the polymer fine particles 1.

[Preparation of Receptive Layer Coating Liquid 5]
5 parts of an isocyanate-based crosslinking agent (for example, Sumidur 3200 manufactured by Sumitomo Bayer Urethane Co., Ltd.) is added to 100 parts of the polymer compound 1, and the whole amount is diluted with methyl ethyl ketone (MEK) so that the solid content becomes 18%. As a result, a receiving layer coating solution 5 was obtained.

[Preparation of Receptive Layer Coating Liquid 6]
A receiving layer coating solution 6 was obtained in the same manner except that the polymer compound 2 was used instead of the polymer compound 1 of the receiving layer coating solution 5.

[Preparation of Receptive Layer Coating Liquid 7]
A receiving layer coating solution 7 was obtained in the same manner except that the polymer compound 3 was used instead of the polymer compound 1 of the receiving layer coating solution 5.

[Preparation of hollow layer coating solution]
To 7.5 parts of a 30% dispersion of styrene-acrylic hollow fine particles (for example, MH8101 manufactured by Nippon Zeon Co., Ltd .: hollow ratio 45%, particle size 1 μm), basic processed gelatin (for example, TYPE-SR manufactured by Nitta Gelatin Co., Ltd.) ) 1.5 parts and 80 parts of ion-exchanged water were added, and the whole was heated to 40 ° C. with stirring. After confirming that the solution was uniform, 0.2 part of an activator (for example, Surfynol 440 manufactured by Air Products) and 0.8 part of an epoxy compound (for example, Denacol EX416B manufactured by Nagase ChemteX) as a hardener Was added to obtain a hollow layer coating solution.

[Preparation of barrier layer coating solution]
110 parts of ion-exchanged water was added to 10 parts of polyvinyl alcohol (for example, PVA-217 manufactured by Kuraray Co., Ltd.) having a polymerization degree of 1700 and a saponification degree of 88%, and dissolved by stirring while raising the temperature to 60 degrees. . Thereafter, the temperature was lowered to 40 ° C., and 0.5 part of a trimethylol melamine-based crosslinking agent (for example, Sumtex Resin M-3 manufactured by Sumitomo Chemical Co., Ltd.) was added to obtain a barrier layer coating solution.

[Preparation of thermal transfer recording medium (hereinafter referred to as thermal transfer recording paper)]
[Preparation of thermal transfer recording paper 1]
A base paper having a basis weight of 140 g / m ² (the paper base 11 shown in FIG. 1) has a surface of 35 g / m ² and a back surface of 25 g / m ² of polyethylene (resin layers 12 and 13 shown in FIG. 1). RC paper to be a support coated with is prepared. The RC paper has a thickness of 200 μm and contains 6% by mass of anatase type titanium in the polyethylene layer (resin layer 12 shown in FIG. 1) on the recording surface side. From the side closer to the paper substrate 11 on the recording surface side of the support, the dry weight solid content of the hollow layer coating solution 1, the resin layer coating solution 1, and the receiving layer coating solution 1 is 10 g / m ² , 0, respectively. .8g / m ^2, simultaneous multilayer by a slide bead coater such that the 2.5 g / m ^2. Thereafter, the temperature of the entire coated product was lowered to 15 ° C. and left for 1 minute, and then dried to produce thermal transfer recording paper 1.
During drying, the drying conditions were adjusted so that the water content after drying was 6 g / m ² . The water content was calculated from the difference in weight before and after the 20 cm square thermal transfer recording paper was dried in an oven at 110 ° C. for 3 minutes.

[Preparation of thermal transfer recording paper 2]
A thermal transfer recording paper 2 was prepared in the same manner as the thermal transfer recording paper 1 except that the receiving layer coating liquid 2 was used instead of the receiving layer coating liquid 1.

[Preparation of thermal transfer recording paper 3]
A thermal transfer recording paper 3 was prepared in the same manner as the thermal transfer recording paper 1 except that the receiving layer coating liquid 3 was used instead of the receiving layer coating liquid 1.

[Preparation of thermal transfer recording paper 4]
A thermal transfer recording paper 4 was prepared in the same manner as the thermal transfer recording paper 1 except that the receiving layer coating liquid 4 was used instead of the receiving layer coating liquid 1.

[Preparation of thermal transfer recording paper 5]
A base material in which a hollow layer and a resin layer are coated on an RC paper as a support is obtained in the same manner as the thermal transfer recording paper 1 except that the receiving layer coating solution is not applied, and then the receiving layer coating solution 5 is obtained. Was separately coated with a wire bar so that the solid content was 2.5 g / m ^2, and thermal transfer recording paper 5 was produced.

[Preparation of thermal transfer recording paper 6]
A thermal transfer recording paper 6 was prepared in the same manner as the thermal transfer recording paper 5 except that the receiving layer coating liquid 6 was used instead of the receiving layer coating liquid 5.

[Preparation of thermal transfer recording paper 7]
A thermal transfer recording sheet 7 was produced in the same manner as the thermal transfer recording sheet 5 except that the receiving layer coating liquid 7 was used instead of the receiving layer coating liquid 5.

[Preparation of thermal transfer recording paper 8]
A base material (bonding paper) in which a 20-micron white pet (for example, Toyobo's Crisper) is bonded to both sides of a 180-micron thick coated paper for printing (for example, Oji Paper's OK Kanto). A thermal transfer recording sheet 8 was produced in the same manner as the thermal transfer recording sheet 1 except that was used.

[Preparation of thermal transfer recording paper 9]
A base material (bonding paper) in which a 20-micron white pet (for example, Toyobo's Crisper) is bonded to both sides of a 180-micron thick coated paper for printing (for example, Oji Paper's OK Kanto). A thermal transfer recording paper 9 was produced in the same manner as the thermal transfer recording paper 6 except that was used.

[Preparation of thermal transfer recording paper 10]
A thermal transfer recording paper 10 was prepared in the same manner as the thermal transfer recording paper 1 except that it was directly applied to a pulp base paper (pulp paper) having a basis weight of 140 g / m ² .

  The thermal transfer recording sheets 1 to 10 obtained as described above were put in a polyethylene bag and aged at room temperature for 24 hours, and the following evaluation was performed.

[Evaluation of gradation characteristics and maximum density]
Using Sony photo printer DPP-SV55 and Adobe Photoshop, signal values of white (R, G, B = 255, 255, 255) and black (R, G, B = 0, 0, 0) A 3 cm × 3 cm printing pattern was printed using The visual reflection density of this print was measured using an optical densitometer RD-918 manufactured by Gretag Macbeth.
In the measurement, the average of five measured values was adopted as the measured value.
When the density of the white background is 0.07 or more, it can be recognized with the naked eye as a fog, which is not preferable as a product. Further, when the density of the black character is 2.0 or less, the black margin is insufficient, which is not preferable as a product.

[Measurement of 20 degree gloss value]
The 20 degree glossiness of the white background part and the black part was measured. For this measurement, for example, a gloss meter VG2000 gloss meter manufactured by Nippon Denka Co., Ltd. was used.
When the glossiness is lower than 60 and the glossiness difference between white and black is 10 or more, the product is not acceptable. Therefore, the glossiness is 60 or more.

[Evaluation of printing unevenness]
A light gray (120, 120, 120) pattern was printed using a Sony photo printer DPP-SV55 and Adobe Photoshop and evaluated visually according to the following criteria.
A: The concentration is uniform throughout.
○: Some unevenness is observed, but it is hardly noticed.
Δ: Unevenness is observed but acceptable.
X: Unevenness is clearly recognized and is not acceptable as a product.
XX: There are a lot of unevenness and it is not acceptable as a product.

  Table 1 shows the gradation characteristics, the maximum density evaluation results, the 20-degree gloss value measurement results, and the print unevenness evaluation results for the thermal transfer recording sheets 1 to 10.

From the results of Table 1 above, the present invention 1 (thermal transfer recording paper sample 1) is poly N, which is a high molecular compound having a lower critical temperature in the image receiving layer 16 in which both sides of the paper substrate are covered with a resin layer. -The thing containing the polymer particle 1 of the star-shaped resin particle of substituted acrylamide is used. Therefore, as described above, in printing with a thermal head below the lower critical point temperature, the polymer chains are dehydrated and self-aggregated, so that the dye transferred from the ink ribbon is difficult to diffuse.
On the other hand, in printing with the energy of the thermal head above the lower critical point temperature, the polymer chains in the dried coating film are spread by thermal motion, the apparent polymer softening point is lowered, and the dye is likely to diffuse.
That is, in the low gradation area printing with low energy, the gradation becomes gentle with respect to the applied energy, so that an image without so-called “fogging” is obtained, and a high density is obtained in the high gradation area.
In addition, since the outermost layer of the plurality of coating layers is composed of a layer containing a polymer compound having a lower critical temperature, after coating the outermost layer coating liquid at the lower critical temperature or higher, the coating film is moved to the lower critical temperature or lower. By lowering the temperature, thickening or gelation mediated by hydrophobic interaction occurs. As a result, a uniform film surface free from blown roughening by dry air can be obtained.
Therefore, the thermal transfer recording medium has a low gradation gradation color cast, good gradation that can achieve high density, and high image uniformity.

The present invention 2 (thermal transfer recording paper 2) is a poly N-substituted acrylamide star resin particle which is a high molecular compound having a lower critical temperature in the image receiving layer, both sides of which are coated with a resin layer. The thing containing the polymer particle 2 of this is used.
Therefore, the same effect as that of the present invention 1 (thermal transfer recording paper sample 1) can be obtained.

Comparative Example 1 (thermal transfer recording paper sample 3) contains polymer particles 3 made of general acrylic emulsion (Em) in the image receiving layer, but does not contain a polymer compound having a lower critical temperature.
Therefore, since the above effect cannot be obtained, the density of the white background is 0.09 among the gradation characteristics, and the fog can be recognized with the naked eye. Further, the glossiness of the white background portion is as low as 40.8. Furthermore, uneven printing is clearly recognized and is not acceptable as a product.

Comparative Example 2 (thermal transfer recording paper sample 4) contains a vinyl chloride emulsion in the image receiving layer, but does not contain a polymer compound having a lower critical temperature.
Therefore, since the above effect cannot be obtained, the density of the white background is 0.11 among the gradation characteristics and can be recognized with the naked eye as a fog. Further, the glossiness of the white background portion is as low as 47.7. Furthermore, uneven printing is clearly recognized and is not acceptable as a product.

The present invention 3 (thermal transfer recording paper sample 5) is a polymer compound of poly N-substituted acrylamide, which is a polymer compound in which both sides of a paper substrate are covered with a resin layer and the image receiving layer has a lower critical temperature. 1 is used.
Therefore, the same effect as that of the present invention 1 (thermal transfer recording paper sample 1) can be obtained.

The present invention 4 (thermal transfer recording paper sample 6) is a polymer compound of poly N-substituted acrylamide, which is a polymer compound in which both sides of a paper substrate are covered with a resin layer and the image receiving layer has a lower critical temperature. 2 is used.
Therefore, the same effect as that of the present invention 1 (thermal transfer recording paper sample 1) can be obtained.

In Comparative Example 3 (thermal transfer recording paper sample 7), the polymer particles 3 contained in the image receiving layer are made of a general acrylic resin. For this reason, the high molecular compound which has a minimum critical temperature is not included.
Therefore, since the above effect cannot be obtained, the density of the white background is 0.1 among the gradation characteristics and can be recognized with the naked eye as a fog. Moreover, the glossiness of a white background part is as low as 40.1. Furthermore, uneven printing is clearly recognized and is not acceptable as a product.

Invention 5 (thermal transfer recording paper sample 8) is a polymer particle of poly N-substituted acrylamide which is a polymer particle having both lower surfaces and a lower critical temperature in the image receiving layer. 1 is used.
Therefore, the same effect as that of the present invention 1 (thermal transfer recording paper sample 1) can be obtained. However, since the paste paper is used, some printing unevenness is recognized, but it is hardly worrisome.

The present invention 6 (thermal transfer recording paper sample 9) is a polymer compound of poly N-substituted acrylamide, which is a polymer particle having both lower surfaces of a paper base material and a resin layer having a lower critical temperature in the image receiving layer. 2 is used.
Therefore, the same effect as that of the present invention 1 (thermal transfer recording paper sample 1) can be obtained. However, since the paste paper is used, some printing unevenness is recognized, but it is hardly worrisome.

  Since Comparative Example 4 (thermal transfer recording paper sample 10) uses pulp paper as the paper substrate, polymer particles of poly N-substituted acrylamide which is a polymer compound having a lower critical temperature in the image receiving layer. Even if 1 is included, black margins are insufficient, glossiness is low, and uneven printing is unacceptable as a product because there are many unevennesses.

  Therefore, with the thermal transfer recording paper having the configuration of the present invention, good gradation characteristics and glossiness can be obtained, and printing unevenness can be allowed.

[Example 2]
In the manufacturing method of the thermal transfer recording paper 1, a thermal transfer recording paper sample is prepared under the conditions shown in Table 2 with the coating liquid temperature at the time of coating, the cooling temperature after coating, and the water content after drying. And aged for 24 hours. Thereafter, the thermal transfer recording paper sample was evaluated in the same manner as in Example 1.

  Table 2 shows the manufacturing conditions and the evaluation results.

As shown in Table 2, the present invention 7 (thermal transfer recording paper 11) is a polymer compound in which both sides of the paper substrate 11 are covered with the resin layers 12 and 13 and the image receiving layer has a lower critical temperature. The poly N-substituted acrylamide star resin particles containing the polymer particles 1 are used. Further, the water content at the time of winding was 3 g / m ² .
Therefore, the same effect as that of the present invention 1 (thermal transfer recording paper sample 1) can be obtained.

The present invention 8 (thermal transfer recording paper 12) is made of poly N-substituted acrylamide, which is a high molecular compound having a lower critical temperature, in which both sides of a paper substrate 11 are covered with resin layers 12 and 13 and an image receiving layer. The thing containing the polymer particle 1 of a star-shaped resin particle is used. Further, the water content at the time of winding was 5.5 g / m ² .
Therefore, the same effect as that of the present invention 1 (thermal transfer recording paper sample 1) can be obtained.

The present invention 9 (thermal transfer recording paper 13) is made of poly N-substituted acrylamide, which is a high molecular compound having a lower critical temperature, in which both sides of a paper substrate 11 are covered with resin layers 12 and 13 and an image receiving layer. The thing containing the polymer particle 1 of a star-shaped resin particle is used. Moreover, the water content at the time of winding was 9 g / m < ² >.
Therefore, the same effect as that of the present invention 1 (thermal transfer recording paper sample 1) can be obtained. However, in the printing unevenness, although the unevenness is partially recognized, it is in a state of little concern.

The present invention 10 (thermal transfer recording paper 14) is made of poly N-substituted acrylamide, which is a high molecular compound having a lower critical temperature, in which both sides of a paper substrate 11 are covered with resin layers 12 and 13 and an image receiving layer. The thing containing the polymer particle 1 of a star-shaped resin particle is used. Further, the water content at the time of winding was 2.5 g / m ² .
Therefore, the same effect as that of the first aspect of the present invention (thermal transfer recording paper sample 1) can be obtained, but the unevenness in printing was in an acceptable state although unevenness was observed.

In the present invention 11 (thermal transfer recording paper 15), both sides of the paper substrate 11 are covered with resin layers 12 and 13, and a poly N-substituted acrylamide which is a polymer compound having a lower critical temperature is contained in the image receiving layer. The thing containing the polymer particle 1 of a star-shaped resin particle is used. Further, the water content at the time of winding was 1.5 g / m ² .
Therefore, the same effect as that of the present invention 1 (thermal transfer recording paper sample 1) can be obtained.

In the present invention 12 (thermal transfer recording paper 16), both sides of the paper substrate 11 are covered with resin layers 12 and 13, and a poly N-substituted acrylamide which is a polymer compound having a lower critical temperature is contained in the image receiving layer. The thing containing the polymer particle 1 of a star-shaped resin particle is used. Moreover, the water content at the time of winding was 12 g / m < ² >.
Therefore, the same effect as that of the present invention 1 (thermal transfer recording paper sample 1) can be obtained.

In Comparative Example 5 (thermal transfer recording paper sample 17), the polymer particles 3 contained in the image receiving layer 16 are made of a general acrylic emulsion (Em). For this reason, the high molecular compound which has a minimum critical temperature is not included.
Therefore, since the above effect cannot be obtained, the glossiness of the white background portion is as low as 40.2. Furthermore, unevenness is clearly recognized and is not acceptable as a product.

In Comparative Example 6 (thermal transfer recording paper sample 18), the polymer particles 3 contained in the image receiving layer 16 are made of a general acrylic emulsion (Em). For this reason, the high molecular compound which has a minimum critical temperature is not included.
Therefore, since the above effect cannot be obtained, the density of the white background of the gradation characteristics is as high as 0.09, and the glossiness of the white background portion is as low as 40.2. Furthermore, unevenness is clearly recognized and is not acceptable as a product.

Thus, the thermal transfer recording sheet of the configuration of the present invention, by winding by adjusting the water content to ^{2g / m 2 ~10g / m 2} , good gradation properties, along with obtaining glossiness, permit uneven printing The range can be made.

  DESCRIPTION OF SYMBOLS 1 ... Thermal transfer recording medium, 11 ... Paper base material, 12, 13 ... Resin layer, 14 ... Hollow layer (layer containing space | gap), 16 ... Image receiving layer (layer containing the high molecular compound which has a minimum critical temperature), 17 ... Multiple coating layers

Claims (5)

A paper substrate;
A resin layer covering both sides of the paper substrate;
Having a plurality of coating layers formed through the resin layer on one side of the paper substrate;
The plurality of coating layers are:
A hollow layer including voids formed in a layer closest to the paper substrate;
The thermal transfer recording medium which has an image receiving layer containing the high molecular compound which has the minimum critical temperature formed in the outermost layer furthest from the said paper base material. The thermal transfer recording medium according to claim 1, wherein the polymer compound having the lower critical temperature is a star-shaped resin particle. The thermal transfer recording medium according to claim 1, wherein the hollow layer comprises organic hollow particles and a cross-linked hydrophilic binder. The thermal transfer recording medium according to claim 1, 2 or 3, further comprising a barrier layer made of only a resin between the hollow layer and the image receiving layer. A step of forming a thermal transfer recording medium by applying a plurality of coating layers on a paper substrate whose both surfaces are covered with a resin layer and then drying the coating layer;
A step of winding the thermal transfer recording medium,
The plurality of coating layers is a polymer in which the coating layer closest to the paper substrate is formed of a hollow layer including voids, and the outermost coating layer farthest from the paper substrate has a lower critical temperature. Formed of an image receiving layer comprising a compound,
A method for producing a thermal transfer recording medium, wherein the water content of the thermal transfer recording medium is adjusted to ² g / m ² to 10 g / m ² and wound.

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