JP4735293B2 - Thermal recording material - Google Patents

Description

The present invention relates to a thermosensitive recording medium having at least a thermosensitive coloring layer and an overcoat layer on a support, and more specifically, no curling occurs when the overcoat layer is cured with active energy rays, and a cutting process is performed after the curing. In particular, the present invention relates to a heat-sensitive recording material which does not generate cracks and can satisfy various performances such as high durability (abrasion resistance and heat resistance), head matching properties, and storage stability.

The heat-sensitive recording material is obtained by reacting a colorless or light-colored basic dye and a developer with heat to obtain a recorded image, and is awarded for various uses. Conventionally, a method of forming an overcoat layer on a heat-sensitive color developing layer has been employed in order to improve the storage stability of the heat-sensitive recording material (prevent fading of the color image). As a method for forming an overcoat layer, a method of applying a chemical-resistant aqueous emulsion resin (see Patent Document 1), a method of applying a water-soluble polymer such as polyvinyl alcohol (see Patent Document 2), etc. are proposed. Has been. Since the aqueous coating needs to be dried at a higher temperature than the organic solvent-based coating, there is a disadvantage that the heat-sensitive recording layer unintentionally develops color in the drying step. Therefore, in order to prevent the heat-sensitive recording layer from developing color in the step of drying the aqueous overcoat layer and to sufficiently cure the aqueous overcoat layer, the setting range of the drying temperature becomes extremely narrow. In addition, if the aqueous overcoat layer is not sufficiently cured, when the resulting thermal recording material is subjected to thermal recording, adhesion between the thermal recording layer and the thermal head of the printer is likely to occur, and printing can be performed smoothly. It becomes impossible (head matching property).

As a method for solving these problems, a method of applying an active energy ray-curable resin on a heat-sensitive recording layer (see Patent Documents 3 and 4) has also been proposed.

By the way, recently, thermal recording materials used for tickets such as tickets, commuter passes, and pass tickets, and prepaid cards are required to have a high degree of scratch resistance and are used in a reversible recording method. In some cases, since recording / erasing by heating is repeated, heat resistance and durability are also required. In applications where such durability is required, methods (such as Patent Documents 5 to 7) of applying an ultraviolet curable resin having a high crosslinking degree as an overcoat layer have been proposed. This is not always satisfactory, such as curling of the recording material, cracking during cutting after curing, and printing marks remaining on the layer.

JP 54-128347 A Japanese Utility Model Publication No. 56-125354 Japanese Examined Patent Publication No. 6-15263 Japanese Patent Publication No.7-119149 Japanese Patent No. 2847520 JP-A-8-310130 JP-A-11-254824

The present invention solves the above-mentioned problem, and the thermal recording material does not curl when the overcoat layer is cured with active energy rays, and cracks also occur during cutting after the layer is cured with active energy rays. An object of the present invention is to provide a heat-sensitive recording material which does not occur and can satisfy various performances such as high durability (abrasion resistance and heat resistance), thermal responsiveness and storage stability.

As a result of intensive studies to solve the above-mentioned problems, the present inventor has obtained an active energy ray containing a specific polymer as the overcoat layer in a thermosensitive recording medium having at least a thermosensitive coloring layer and an overcoat layer on the support. It has been found that the object can be achieved by using a curable resin composition, and the present invention has been completed.

That is, the present invention
1. In a thermosensitive recording medium having at least a thermosensitive coloring layer and an overcoat layer on a support, an α, β-unsaturated monocarboxylic acid is added to an epoxy group-containing (meth) acrylate polymer as an overcoat layer. An active energy ray-curable resin composition containing a reactive polymer (A) that is a reaction product and has a (meth) acrylic equivalent of 200 to 350 g / eq and a weight average molecular weight of 5,000 to 150,000 is used. A thermal recording material characterized by
2. 1. The reactive polymer (A) has a (meth) acrylic equivalent of 200 to 270 g / eq and a weight average molecular weight of 10,000 to 100,000. A thermal recording material according to claim 1,
3. The epoxy group-containing (meth) acrylate polymer is a copolymer of the (meth) acrylate homopolymer or an α, β-unsaturated monomer not containing the (meth) acrylate and a carboxyl group. 1. Or 2. A thermal recording material according to claim 1,
4). The epoxy group-containing (meth) acrylate used for the reactive polymer (A) is at least one selected from the group consisting of glycidyl (meth) acrylate, alicyclic epoxy group-containing (meth) acrylate, and (meth) acrylic acid alkyl glycidyl ether. 1. Seed ~ 3. The heat-sensitive recording material according to any one of,
5. The active energy ray-curable resin composition comprises 50 to 100 parts by weight of a reactive polymer (A), 0 to 40 parts by weight of a (meth) acrylate (B) having 3 or more functional groups, and a (meth) acrylate having 2 or less functional groups. (C) It consists of 0 to 10 parts by weight (however, the sum of (A), (B) and (C) is 100 parts by weight). ~ 4. A heat-sensitive recording material according to any one of
6). 1. A barrier layer was provided between the thermosensitive coloring layer and the overcoat layer . ~ 5. A heat-sensitive recording material according to any one of
7). 1. A back coat layer is provided on the back surface of the support. ~ 6. A heat-sensitive recording material according to any one of
About.

  According to the present invention, the thermal recording material does not curl when the overcoat layer is cured with active energy rays, and cracks do not occur during cutting after the layer is cured with active energy rays. It is possible to provide a heat-sensitive recording material that can satisfy various performances such as durability (abrasion resistance and heat resistance), thermal response, and storage stability.

  The heat-sensitive recording material of the present invention has a structure in which a heat-sensitive coloring layer and a specific overcoat layer are provided in order on a support, and a barrier layer is provided between the heat-sensitive coloring layer and the overcoat layer as necessary. The provided structure may be sufficient.

The support in the heat-sensitive recording material of the present invention is not particularly limited, and various known materials can be appropriately selected depending on the application. For example, acrylic resin, polycarbonate resin, vinyl chloride resin, urethane resin can be selected. Resins, polyester resins, and the like can be used. The shape of the support is not particularly limited and can be appropriately selected according to the application. In general, sheets such as paper, film, and synthetic paper are used.

The heat-sensitive coloring layer in the heat-sensitive recording material of the present invention is not particularly limited, and can be appropriately selected from various known materials depending on the application. The thermosensitive coloring layer is mainly composed of a colorless or light-coloring coloring compound, preferably a basic dye, and a color developing compound capable of developing color when heated. Depending on the case, sensitizers, fillers, other additives and the like can be contained. The types of the color forming compound and the color developing compound are not particularly limited, and various known compounds can be appropriately selected and used. Color recording in the thermosensitive color developing layer is based on a chemical reaction that occurs when one or both of the color developing compound and the color developing compound melt and come into contact with each other. Enables reversible recording. The thermosensitive coloring layer was formed by dispersing and pulverizing the coloring compound and the developing compound, respectively, mixing both, and further adding a binder, a sensitizer, a filler, and other components to prepare a coating solution. Thereafter, the coating liquid is applied on a support.

In forming the thermosensitive coloring layer, the color developing compound is 1 to 50% by weight, preferably 5 to 30% by weight, the color developing compound is 1 to 80% by weight, preferably 5 to 40% by weight, and the binder is 1%. ˜90 wt%, filler is 0 to 80 wt%, and other lubricants, surfactants, antifoaming agents, ultraviolet absorbers, etc. are used in arbitrary proportions, for example, 0 to 30 wt% each ( % By weight is the weight ratio of each component in the thermosensitive coloring layer).

Examples of the chromogenic compound include a fluorane compound, a triarylmethane compound, a spiropyran compound, a diphenylmethane compound, a thiazine compound, a lactam compound, and a fluorene compound, which can be used alone or in combination. .

Examples of the color developing compound include p-octylphenol, p-tert-butylphenol, 2,2-bis (p-hydroxyphenyl) propane, 1,1-bis- (p-hydroxyphenyl) cyclohexane, 4,4 ′. -Thiobisphenol, 4,4'-sulfonyldiphenol, bis- (3-allyl-4-hydroxyphenyl) sulfone, novolac type phenol resin, benzyl p-hydroxybenzoate, ethyl p-hydroxybenzoate, 4-hydroxyphthalate Dimethyl acid, ethyl 5-hydroxyisophthalate, 3,5-di-tert-butylsalicylic acid, 3,5-di-α-methylbenzylsalicylic acid, 1,7-di (hydroxyphenylthio) -3,5-dioxa Heptane, 4-isopropoxy-4'-hydroxydiphenylsulfone Bis (4-hydroxyphenyl) acetate, bis (4-hydroxyphenyl) butyl acetate, bis (4-hydroxyphenyl) acetic acid benzyl etc., also in the aromatic carboxylic acids, polyvalent metal salts thereof. These color developing compounds can also be used alone or in combination.

The binder as a component for forming the thermosensitive coloring layer includes methylcellulose, methoxycellulose, hydroxyethylcellulose, carboxymethylcellulose, polyvinyl alcohol, carboxyl group-modified polyvinyl alcohol, acetoacetylated polyvinyl alcohol, silica modified polyvinyl alcohol, acrylic acid / styrene copolymer. Alkali salt of polymer, polyvinylpyrrolidone, polyacrylamide, polyacrylic acid, starch and derivatives thereof, casein, gelatin, alkali salt of styrene / maleic anhydride copolymer, iso (or diiso) butylene / maleic anhydride copolymer Water-soluble materials such as alkali salts of polyvinyl acetate, polyvinyl acetate, vinyl chloride / vinyl acetate copolymer, polystyrene, styrene / butadiene / acrylic acid copolymer, etc. Water-soluble emulsion is used.

The overcoat layer obtained by using the active energy ray-curable resin composition is excellent in thermal printer head matching, but further improves the performance, further improves the wear resistance, In order to adjust the gloss of the coat layer, a filler can be appropriately used from the viewpoint of functioning as a so-called matting agent. Examples of the filler include calcium carbonate, magnesium carbonate, magnesium oxide, silica, white carbon, talc, clay, alumina, magnesium hydroxide, aluminum oxide, barium sulfate, polystyrene resin, urea-formalin resin, and the like. In addition, what is necessary is just to use dispersers, such as a ball mill, a roll mill, a sand mill, and a dissolver, in order to disperse | distribute this filler in a reactive polymer (A).

Moreover, you may mix | blend a dispersing agent and a silane coupling agent in an active energy ray curable resin composition as needed. Sensitizers may also be blended, such as waxes such as animal and vegetable waxes, polyethylene waxes, synthetic waxes, higher fatty acids, higher fatty acid amides, higher fatty acid metal salts, acetyl compounds of aromatic amines, aromatic ethers. Examples thereof include compounds and biphenyl derivatives that are solid at room temperature and have a melting point of about 80 ° C. or higher. Furthermore, as other additives, lubricants such as zinc stearate, calcium stearate and aluminum stearate, various other surfactants, antifoaming agents and the like can be added as necessary.

As a method for forming the thermosensitive coloring layer on the support, for example, after pulverizing and dispersing each of the above components by a dispersing machine such as a ball mill, an attritor, and a sand mill, Coating may be performed using a bar coater, an air knife coater, a gravure coater, a roll coater or the like so as to be about 40 g / m ² and dried.

The overcoat layer in the heat-sensitive recording material of the present invention is provided to protect the support and the heat-sensitive color developing layer obtained according to the above from scratches and accidental color development. The material of the overcoat layer is curability when irradiated with active energy rays, prevention of curling and cracking during curing, durability of the resulting cured film (wear resistance, heat resistance), thermal response, storage stability It must be carefully determined in consideration of various requirements. In order to achieve the object and effect of the present invention, a reaction product obtained by adding an α, β-unsaturated monocarboxylic acid to an epoxy group-containing (meth) acrylate polymer and having a (meth) acrylic equivalent Contains a reactive polymer (A) that is 200 to 350 g / eq, preferably 200 to 270 g / eq, and has a weight average molecular weight of 5,000 to 150,000, preferably 10,000 to 100,000. It is essential to use an active energy ray-curable resin composition.

The (meth) acryl equivalent of the reactive polymer (A) is mainly determined from the curability at the time of active energy ray irradiation, and when the amount is larger than 350 g / eq, the abrasion resistance of the cured layer after the active energy ray irradiation. Abrasion becomes insufficient, and synthesis of less than 200 g / eq is not easy. The molecular weight of the reactive polymer (A) takes into account the ease of synthesis of the polymer, the coating workability during the formation of the overcoat layer, the durability of the cured film of the overcoat layer (wear resistance, heat resistance), etc. When the weight average molecular weight is less than 5,000, the synthesis thereof is not easy, and when it exceeds 150,000, the viscosity of the resulting polymer becomes too high, and the coating workability when forming the overcoat layer is increased. descend.

The reactive polymer (A) is obtained by adding an α, β-unsaturated monocarboxylic acid to an epoxy group-containing (meth) acrylate polymer so that the (meth) acryl equivalent and the weight average molecular weight satisfy the above ranges. Is obtained. The epoxy group-containing (meth) acrylate polymer is a homopolymer obtained by polymerizing an epoxy group-containing (meth) acrylate monomer; does not contain an epoxy group-containing (meth) acrylate monomer and a carboxyl group A copolymer obtained by copolymerizing an α, β-unsaturated monomer is applicable. The content (% by weight) of the α, β-unsaturated monomer that does not contain a carboxyl group in the reactive polymer (A) obtained from the copolymer is the same as that of each component of the reactive polymer (A). Since there are fluctuation factors such as the kind of the monomer and the (meth) acrylic equivalent (setting value) of the reactive polymer (A), it cannot be uniquely determined. Therefore, in the present invention, the content of the α, β-unsaturated monomer not containing a carboxyl group is appropriately determined so that the obtained reactive polymer (A) satisfies the range of the (meth) acryl equivalent. do it.

Among the constituent monomers of the reactive polymer (A), the epoxy group-containing (meth) acrylate is not particularly limited. For example, glycidyl (meth) acrylate, alicyclic epoxy group-containing (meth) acrylate, (meth) Examples include alkyl glycidyl ether acrylate.

Examples of the alicyclic epoxy group-containing (meth) acrylate include, for example, the general formula 1:

(Wherein n is an average value of 0 to 1 and R is a hydrogen atom or a methyl group). Examples of those commercially available products include cyclomers M100, A200, M101 ( Daicel Chemical Industries, Ltd.) can be obtained. Moreover, as alkyl glycidyl ether of (meth) acrylic acid, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate and other hydroxy (meth) acrylate and epichlorohydrin condensates And various known compounds. Any of the above-mentioned epoxy group-containing (meth) acrylates can be used alone or in appropriate combination. Among these compounds, glycidyl (meth) acrylate is preferable from the viewpoints of availability, polymerization reactivity, and price.

Further, among the constituent monomers of the reactive polymer (A), the α, β-unsaturated monomer not containing a carboxyl group is not particularly limited. For example, (meth) acrylic acid esters, styrenes, acetic acid Various known compounds such as vinyl and acrylonitrile can be used. These compounds can be used alone or in appropriate combination. If an α, β-unsaturated monomer containing a carboxyl group is used, crosslinking occurs during the copolymerization reaction with the epoxy group-containing (meth) acrylate, which is not preferable because the product becomes highly viscous or gelled. .

Among the constituent monomers of the reactive polymer (A), the α, β-unsaturated monocarboxylic acid to be added to the epoxy group-containing (meth) acrylate polymer includes (meth) acrylic acid, The compounds can be used alone or in combination as appropriate. For example, when α, β-unsaturated dicarboxylic acid such as itaconic acid, maleic acid or maleic anhydride is used, crosslinking occurs during the copolymerization reaction with the epoxy group-containing (meth) acrylate, resulting in a high product. It is not preferable because it becomes viscous or gelled.

There is no limitation in particular as a manufacturing method of reactive polymer (A), A conventionally well-known method is employable. The production of the epoxy group-containing (meth) acrylate polymer can be carried out by (1) heating the epoxy group-containing (meth) acrylate in the presence of a radical polymerization initiator to homopolymerize, or (2) the (meth) A radical polymerization initiator is prepared by charging the epoxy group-containing (meth) acrylate and the α, β-unsaturated monomer not containing the carboxyl group in predetermined amounts so that the acrylic equivalent and the weight average molecular weight satisfy the above ranges. It may be copolymerized by heating in the presence of. The polymerization temperature is not particularly limited, but is usually about 60 to 140 ° C., and the polymerization may be performed in an inert gas atmosphere as necessary. The epoxy group-containing (meth) acrylate polymer thus obtained is subjected to an addition reaction with the α, β-unsaturated monocarboxylic acid so that the (meth) acryl equivalent and the weight average molecular weight satisfy the above ranges. You can do it. In the addition reaction, in order to prevent accidental polymerization of the α, β-unsaturated monocarboxylic acid, it is preferable to use an air or oxygen atmosphere. In the reaction, the temperature is usually in the range of about 80 to 120 ° C., and a basic catalyst such as triphenylphosphine or diethylenetriamine may be added as necessary.

In addition to the reactive polymer (A), the active energy ray-curable composition for forming the overcoat layer is about 0 to 40 parts by weight, preferably 10 to 30 parts by weight of a tri- or higher functional (meth) acrylate (B). Part and a bifunctional or lower (meth) acrylate (C) of about 0 to 10 parts by weight, preferably 5 parts by weight or less (total of (A), (B) and (C) is 100 parts by weight) Can do. The content of the trifunctional or higher functional (meth) acrylate (B) is determined in consideration of curling and cracking suppression of the resulting thermal recording material, durability of the cured layer, and the content exceeds 40 parts. In some cases, cracks may occur in the cured layer during the cutting process or over time, and the resulting cured layer tends to be too hard and the thermal recording material tends to curl. On the other hand, when the content is less than 10 parts, the active energy ray curability tends to be slightly inferior, and when the active energy ray is not sufficiently irradiated, the adhesion to the support and the durability of the cured layer are lowered. There is a case. The content of the bifunctional or lower (meth) acrylate (C) is also determined from the same viewpoint as in the above (B), and when the content exceeds 5 parts, the scratch resistance of the cured layer is reduced. There is a tendency that fog is likely to occur on the thermosensitive coloring layer.

The coating amount and film thickness of the overcoat layer in the heat-sensitive recording material of the present invention can be appropriately determined according to the use conditions, but usually the coating amount is about ² to 5 g / m ² and the dry film thickness is 1 to 1. It is about 2 μm. When the film thickness of the overcoat layer is too small, the wear resistance tends to decrease, and when the film thickness is excessive, the thermal response tends to decrease.

In the thermosensitive recording material of the present invention, a barrier layer may be provided between the thermosensitive coloring layer and the overcoat layer. The barrier layer is a resin layer for protecting the support and the thermosensitive coloring layer from external factors (water, sunlight, chemicals, etc.), for example, to improve the adhesion between the layers. Thermoplastic resins such as urethane resins, melamine-based and epoxy-based thermosetting resins, and vinyl chloride copolymer resins can be used. As a method for forming the barrier layer , the same coating method as used in the preparation of the thermosensitive coloring layer and the overcoat layer can be applied.

In the heat-sensitive recording material of the present invention, a backcoat layer can be provided in order to most effectively eliminate curling at the time of curing the overcoat layer. The material for the backcoat layer is not particularly limited, but it is preferable to use an active energy ray-curable resin having the same degree of curing shrinkage as the overcoat layer. Specific examples of the material for forming the overcoat layer include a resin composition comprising a reactive oligomer such as urethane (meth) acrylate, epoxy (meth) acrylate, ester (meth) acrylate, or a polymerizable (meth) acrylic functional diluent. I can raise things. Moreover, a well-known photoinitiator, a sensitizer, an additive, a solvent, etc. can be mix | blended with this resin composition as needed.

The coating amount and film thickness of the backcoat layer in the heat-sensitive recording material of the present invention can be appropriately determined according to the use conditions, but the coating amount is usually about ² to 5 g / m ² . When the film thickness of the back coat layer is too small, the curl prevention effect tends to be reduced, and when the film thickness is excessive, the film tends to curl on the back side. As a method for forming the backcoat layer, the same coating method as used in the preparation of the thermosensitive coloring layer and the overcoat layer can be applied.

 EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited only to these examples. In each example, all parts and% are based on weight unless otherwise specified.

(Preparation of reversible thermosensitive recording layer coating solution)
40 parts of 3-diethylamino-6-methyl-7-anilinofluorane and 100 parts of N- (p-hydroxyphenyl-N′-octadecylurea were added to 8% polyvinyl acetal (manufactured by Sekisui Chemical Co., Ltd., trade name “BL -1 ", acetalization degree 63 mol%) and a tetrahydrofuran (THF) solution 9100 parts were ground by a paint conditioner to prepare a reversible thermosensitive recording layer coating solution.

(Preparation of reversible thermosensitive recording layer)
After 29 parts of isocyanate (trade name “Coronate L”, manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to the coating liquid for the reversible thermosensitive recording layer obtained above, the solid content of the polyethylene terephthalate (PET) sheet was 4. It applied so that it might become 0 g / m < ² >. The film was dried at 60 ° C. for 24 hours and treated with a super calendar to obtain a reversible thermosensitive recording layer.

(Synthesis of reactive polymer (A))
Synthesis example 1
10 parts of glycidyl methacrylate (hereinafter referred to as GMA) in a reactor equipped with a stirrer, a cooling pipe, a dropping funnel and a nitrogen introduction pipe, 40 parts of butyl acetate as a solvent, 2,2′-azobis (2-methylbutyronitrile) ) {Hereinafter referred to as ABN-E} 0.4 parts were added, and the mixture was kept at 85-90 ° C. for 30 minutes under a nitrogen stream, and then 30 parts of GMA and 1.2 parts of ABN-E were added dropwise over 2 hours from the dropping funnel. After incubating at the same temperature for 3 hours, 0.4 part of ABN-E was added and the mixture was incubated for 30 minutes. Thereafter, the temperature was raised to 120 ° C. and kept warm for 2.5 hours. After cooling to 60 ° C., the nitrogen inlet tube was replaced with an air inlet tube, and after mixing and mixing 20.3 parts of acrylic acid (hereinafter referred to as AA), 0.09 part of methoquinone and 0.24 part of triphenylphosphine, air The temperature was raised to 110 ° C. under bubbling. After incubating at the same temperature for 8 hours, 0.03 part of methoquinone and 0.03 part of finothiazine are charged, cooled, and ethyl acetate is added so that the non-volatile content is 50%, whereby the reactive polymer (A1) solution is obtained. Obtained. The reactive polymer (A) contained in the solution had an acrylic equivalent of 214 g / eq and a weight average molecular weight of 40,000. (Based on styrene conversion by GPC)

Synthesis example 2
In Synthesis Example 1, the reaction was similarly performed except that 0.4 part of ABN-E charged in the reactor main body was changed to 0.25 part and 1.2 part of ABN-E charged in the dropping funnel was changed to 0.75 part. A solution was obtained. The polymer contained in the polymer B solution had an acrylic equivalent of 214 g / eq and a weight average molecular weight of 95,000.

Synthesis example 3
In Synthesis Example 1, 10 parts of GMA is 8 parts of GMA and 2 parts of methyl methacrylate (hereinafter referred to as MMA), 30 parts of GMA charged to the dropping funnel is 24 parts of GMA and 6 parts of MMA, and the AA charge is from 20.3 parts. A reactive polymer (A3) solution was obtained by reacting in the same manner except that the amount was changed to 16.2 parts. The reactive polymer (A3) contained in the solution had an acrylic equivalent of 250 g / eq and a weight average molecular weight of 32,500.

Synthesis example 4
In Synthesis Example 1, instead of GMA, alicyclic epoxy group-containing (meth) acrylate [Cyclomer M200 (manufactured by Daicel Chemical Industries, Ltd.)] was used (however, the amount used was the same as the amount of GMA used in Synthesis Example 1) The same) except that the AA charge was changed from 20.3 parts to 14.7 parts to obtain a reactive polymer (A4) solution. The reactive polymer (A4) contained in the solution had an acrylic equivalent of 268 g / eq and a weight average molecular weight of 35,000.

Synthesis example 5
In Synthesis Example 1, 10 parts of GMA charged into the reactor main body was changed to 5 parts of GMA and 5 parts of methyl methacrylate (hereinafter referred to as MMA), 30 parts of GMA charged into the dropping funnel were changed to 15 parts of GMA and 15 parts of MMA, and the AA charge was further increased. A reactive polymer (A5) solution for comparison was obtained by reacting in the same manner except that the amount was changed from 20.3 parts to 10.2 parts. The reactive polymer (A5) contained in the solution had an acrylic equivalent of 356 g / eq and a weight average molecular weight of 29,800.

(Coating of overcoat layer)
The reactive polymers (A) (A1 to A3) obtained in Synthesis Examples 1 to 3, polyfunctional monomers, additives, and the like are blended in the proportions shown in Table 1, and various active energy ray-curable compositions are prepared. Prepared. Next, each of the compositions was applied on the coated sheet prepared above so as to have a dry coating film of 1.0 g / m ² and dried, and then cured using an ultraviolet irradiation device (120 w / cm, 30 mJ / cm ² ) to obtain a reversible thermosensitive recording material having an overcoat layer.

In Table 1, DPHA is dipentaerythritol hexaacrylate (manufactured by Toagosei Co., Ltd., trade name “Aronix M400”), BS-575 is polyfunctional urethane acrylate (Arakawa Chemical Industries, Ltd.), and HPA is Hydroxypropyl acrylate (manufactured by Osaka Organic Chemical Co., Ltd.), photoinitiator is 1-hydroxy-cyclohexyl-phenylketone (manufactured by Ciba Specialty Chemicals, trade name “IRGACURE184”), matting agent is synthetic amorphous silica ( Tosoh Silica Co., Ltd., trade name “Nipsil E220A”).

Example 8
A resin composition for backcoat layer formation comprising the reactive polymer (A1) / DPHA / ethyl acetate / photoradical initiator = 60/20/20/4 (parts by weight) was prepared and prepared in Example 3. The composition is coated on the back surface of the coated sheet so that the dried coating film is 1.0 g / m ² , dried, and then cured (120 w / cm, 30 mJ / cm ² ) using an ultraviolet irradiation device. Thus, a reversible thermosensitive recording material having a backcoat layer was obtained.

Test 1 (color density = thermal response)
Using a thermal facsimile printing tester TH-PMD manufactured by Okura Electric Co., Ltd. equipped with a print head KJT-256-8MGF1 manufactured by Kyocera Corporation, an applied pulse of 1.1 milliseconds and an applied voltage of 26 volts were used. Then, printing was performed on each of the various reversible thermosensitive recording materials obtained in Examples 1 to 7 and Comparative Examples 1 to 4, and the density of each color image obtained was measured using a densitometer Macbeth RD918 (manufactured by Gretag Macbeth). Measured.

Test 2 (image erasability)
Applied pulse 1.1 using a thermal facsimile printing tester (print head: manufactured by Kyocera Corporation, trade name “KJT-256-8MGF1”, apparatus: product of Okura Electric Co., Ltd., trade name “TH-PMD”) Each of the various reversible thermosensitive recording materials was printed in milliseconds under the condition of an applied voltage of 26 volts, and this was heated for 1 second at 120 ° C. using a heat stamp, and then the concentration was adjusted in the same manner as in Test 1. It was measured.

Test 3 (Change in color density with time = image stability)
Under the same conditions as in Test 2, each of the various reversible thermosensitive recording materials was printed and stored for 24 hours in an atmosphere at a temperature of 50 ° C. and a relative humidity of 20%. The density was measured, and the image residual ratio was calculated by the following formula A = (C / B) × 100.

In the above equation, A: image remaining rate (%), B: image density before test, and C: image density after test.

Test 4 (repeated durability)
Using a thermal printer (manufactured by Panasonic Communications Co., Ltd., trade name “CARD READER WRITER KUR-3071”) while driving the erasing bar at 140 ° C. under the conditions corresponding to the printing energy of 0.826 mj / dot With respect to the reversible multicolor thermosensitive recording material, erasing and printing were repeated 100 times, and then the density of the colored portion was measured in the same manner as in Test 1. Moreover, the protective layer surface after a test was observed visually. The case where no deterioration was observed on the surface of the protective layer was evaluated as ◯, the case where the surface of the protective layer was slightly cracked was evaluated as Δ, and the case where the protective layer was deteriorated and discoloration or peeling was marked was evaluated as X.

Test 5 (cured curling property)
Each of the various reversible thermosensitive recording materials is cut into 10 cm squares of length and width, and the degree of lifting of the four corners is measured. The average value is 2 mm or less, the average is 2 mm or less, the one exceeding 2 mm is 10 mm or less Evaluation was made with a value of 30 mm or less as Δ and a value exceeding 30 mm as ×.

Test 6 (Crack resistance)
Each of the various reversible thermosensitive recording materials was cut with a cutter knife, the cut portion was observed with a microscope, ○ where no cracks were observed, ○ where there were slight cracks, and Δ The case where dropout was observed was evaluated as x.

Test 7 (Abrasion resistance)
The various reversible thermosensitive recording materials were each rubbed with steel wool loaded with a load of 200 g / cm ² , evaluated as “◯” when there was no change, “Δ” when slightly damaged, and “×” when severely damaged.

Table 2 shows the test results.

Claims (7)

In a thermosensitive recording medium having at least a thermosensitive coloring layer and an overcoat layer on a support, an α, β-unsaturated monocarboxylic acid is added to an epoxy group-containing (meth) acrylate polymer as an overcoat layer. An active energy ray-curable resin composition containing a reactive polymer (A) that is a reaction product and has a (meth) acrylic equivalent of 200 to 350 g / eq and a weight average molecular weight of 5,000 to 150,000 is used. A heat-sensitive recording material. The thermosensitive recording material according to claim 1, wherein the reactive polymer (A) has a (meth) acrylic equivalent of 200 to 270 g / eq and a weight average molecular weight of 10,000 to 100,000. The epoxy group-containing (meth) acrylate polymer is a copolymer of the (meth) acrylate homopolymer or an α, β-unsaturated monomer not containing the (meth) acrylate and a carboxyl group. The heat-sensitive recording material according to claim 1 or 2. The epoxy group-containing (meth) acrylate used for the reactive polymer (A) is at least one selected from the group consisting of glycidyl (meth) acrylate, alicyclic epoxy group-containing (meth) acrylate, and (meth) acrylic acid alkyl glycidyl ether. The thermosensitive recording material according to claim 1, which is a seed. The active energy ray-curable resin composition comprises 50 to 100 parts by weight of a reactive polymer (A), 0 to 40 parts by weight of a (meth) acrylate (B) having 3 or more functional groups, and a (meth) acrylate having 2 or less functional groups. The thermosensitive recording material according to any one of claims 1 to 4, which comprises (C) 0 to 10 parts by weight (provided that the sum of (A), (B) and (C) is 100 parts by weight). . The heat- sensitive recording material according to claim 1, wherein a barrier layer is provided between the heat-sensitive coloring layer and the overcoat layer . The thermosensitive recording material according to any one of claims 1 to 6, wherein a back coat layer is provided on the back surface of the support.