HEAT-SENSITIVE RECORDING MATERIAL

Abstract

Disclosed is a heat-sensitive recording material comprising an undercoat layer and a heat-sensitive recording layer formed in this order on a support, the undercoat layer containing hollow plastic particles and a binder, the heat-sensitive recording layer containing a leuco dye and a developer, and the heat-sensitive recording material having an elastic modulus of 200 N/mm.sup.2 or less as measured by a nanoindentation method.

Claims

1. A heat-sensitive recording material comprising an undercoat layer and a heat-sensitive recording layer formed in this order on a support, the undercoat layer containing hollow plastic particles and a binder, the heat-sensitive recording layer containing a leuco dye and a developer, and the heat-sensitive recording material having an elastic modulus of 200 N/mm.sup.2 or less as measured by a nanoindentation method.

2. The heat-sensitive recording material according to claim 1, wherein the undercoat layer contains hollow plastic particles having an average particle diameter of 5.0 μm or more.

3. The heat-sensitive recording material according to claim 2, wherein the undercoat layer contains the hollow plastic particles having an average particle diameter of 5.0 μm or more in a proportion of 50 mass % or less, based on the total solids content of the undercoat layer.

4. The heat-sensitive recording material according to claim 2, wherein the undercoat layer contains the hollow plastic particles having an average particle diameter of 5.0 μm or more in a proportion of 30 mass % or less, based on the total solids content of the undercoat layer.

5. The heat-sensitive recording material according to claim 1, wherein the undercoat layer contains a binder having a glass transition temperature of −10° C. or less.

6. The heat-sensitive recording material according to claim 1, wherein the binder in the undercoat layer contains latex.

7. The heat-sensitive recording material according to claim 6, wherein the undercoat layer contains the latex in a proportion of 25 mass % or more, based on the total solids content of the undercoat layer.

Description

EXAMPLES

[0056] The present invention is described below in more detail with reference to Examples. However, the present invention is not. limited to these Examples. In the Examples, “parts” and “%” represent “parts by mass” and “percent by mass,” respectively, unless otherwise specified.

Example 1

(1) Preparation of Coating Liquid for Undercoat Layer

[0057] A coating liquid for an undercoat layer was prepared by mixing and stirring 154 parts of hollow plastic particles A (trade name: 461WE20, D50: 20 μm, produced by AkzoNobel, solids content: 13.0%), 162 parts of hollow plastic particles B (trade name: Ropaque SN-1055, produced by The Dow Chemical Company, D50: 1.0 μm, solids content: 26.5%), 63 parts of styrene-butadiene latex (trade name: Nalstar SR-116, produced by Nippon A & L Inc., solids content: 50.5%, Tg: −28° C.), and 2 parts of carboxymethyl cellulose (trade name: Cellogen AG gum, produced by DES Co. Ltd.) were mixed with stirring to obtain a coating liquid for an undercoat layer.

(2) Preparation of Leuco Dye Dispersion (Liquid A)

[0058] 40 parts of 3-di-(n-butyl)amino-6-methyl-7-anilinofluoran, 40 parts of a 10% aqueous solution of polyvinyl alcohol (degree of polymerization: 500, degree of saponification: 88%), and 20 parts of water were mixed. The resulting mixture was pulverized with a sand mill (produced by Imex Co., Ltd., a sand grinder) to a median diameter of 0.5 μm as measured with a SALD2200 laser diffraction particle size distribution analyzer (produced by Shimadzu Corporation), thus obtaining a leuco dye dispersion (dispersion A).

(3) Preparation of Developer Dispersion (Liquid B-1)

[0059] 40 parts of 4-hydroxy-4′-isopropoxydiphenyl sulfone (D8 produced by Nippon Soda Co., Ltd.), 40 parts of a 10% aqueous solution of polyvinyl alcohol (degree of polymerization: 500, degree of saponification: 88%), and 20 parts of water were mixed. The resulting mixture was pulverized with a sand mill (produced by Imex Co., Ltd., a sand grinder) to a median diameter of 1.0 μm as measured with a SALD2200 laser diffraction particle size distribution analyzer (produced by Shimadzu Corporation), thus obtaining a developer dispersion (liquid B).

(4) Preparation of Sensitizer Dispersion (Liquid C)

[0060] 40 parts of oxalic acid di(p-methylbenzyl) ester (trade name: HS-3520, produced by DIC Corporation), 40 parts of a 10% aqueous solution of polyvinyl alcohol (degree of polymerization: 500, degree of saponification: 88%), and 20 parts of water were mixed. The mixture was pulverized with a sand mill (produced by Imex Co., Ltd., a sand grinder) to a median diameter of 1.0 μm as measured with a SALD2200 laser diffraction particle size distribution analyzer (produced by Shimadzu Corporation), thus obtaining a sensitizer dispersion (dispersion C).

(5) Preparation of Coating Liquid for Heat-Sensitive Recording Layer

[0061] A composition comprising 29.5 parts of liquid A, 59.1 parts of liquid B, 45.5 parts of liquid C, 45 parts of a 10% aqueous solution of completely saponificated polyvinyl alcohol (product name: PVA110, degree of saponification: 99 mole %, average degree of polymerization: 1000, produced by Kuraray Co., Ltd.), 9.4 parts of a butadiene-based copolymer latex (product. name: L-1571, solids content: 48%, produced by Asahi Kasei Corporation) , 25.1 parts of light calcium, carbonate (trade name: Brilliant-15, produced by Shiraishi Kogyo Co., Ltd.), 11.7 parts of paraffin wax (trade name: Hydrin L-700, produced by Chukyo Yushi Co., Ltd., solids content: 30%), 2 parts of adipic acid dihydrazide (produced by Otsuka Chemical Co., Ltd.), and 120 parts of water was mixed with stirring to obtain a coating liquid for a heat-sensitive recording layer.

(6) Preparation of Coating Composition for Protective Layer

[0062] A composition comprising 300 parts of a 10% aqueous solution of acetoacetyl-modified polyvinyl alcohol (trade name: Gosenex Z-200, saponification degree: 99.4 mol %, average degree of polymerization: 1000, modification degree: 5 mol %, produced by The Nippon Synthetic Chemical Industry Co., Ltd.), 63 parts of kaolin (trade name: Hydragloss 90, produced by KaMin LLC), 0.5 part of polyethylene wax (trade name: Chemipearl W-400, produced by Mitsui Chemicals Inc., solids content: 40%), and 114.5 parts of water was mixed with stirring to obtain a coating liquid for a protective layer.

(7) Production of Heat-Sensitive Recording Material

[0063] A coating liquid for an undercoat layer, a coating liquid for a heat-sensitive recording layer, and a coating liquid for a protective layer were applied in amounts after drying of 3.0 g/m.sup.2, 4.0 g/m.sup.2, and 2.0 g/m.sup.2, respectively, to one surface of high quality paper having a basis weight of 60 g/m.sup.2, and dried to form an undercoat layer, a heat-sensitive recording layer, and a protective layer in this order. The obtained product was then super-calendared to smooth the surface, thus obtaining a heat-sensitive recording material. The proportion of hollow plastic particles having an average particle diameter of 5.0 μm or more in the undercoat layer was 20 mass %.

Example 2

[0064] A heat-sensitive recording material was obtained in the same manner as in Example 1 except that in the preparation of the coating liquid for an undercoat layer in Example 1, 308 parts of hollow particles A and 87 parts of hollow particles B were used in place of 154 parts of hollow particles A and 162 parts of hollow particles B. The proportion of hollow plastic particles having an average particle diameter of 5.0 μm or more in the undercoat layer was 40 mass %.

Example 3

[0065] A heat-sensitive recording material was obtained in the same manner as in Example 1 except that in the preparation of the coating liquid for an undercoat layer in Example 1, 32 parts of styrene-butadiene latex was used in place of 63 parts, and 53 parts of modified starch (trade name: Petrocoat C-8, produced by Nippon Starch Chemical Co., Ltd., solids content: 30%) was added.

Example 4

[0066] A heat-sensitive recording material was obtained in the same manner as in Example 1 except that in the preparation of the coating liquid. for an undercoat layer in Example 1, 67 parts of L-1571 (trade name, produced by Asahi Kasei Corporation, solids content 48%, Tg: 3° C.) was used in place of 63 parts of the styrene-butadiene latex.

Example 5

[0067] A heat-sensitive recording material was obtained in the same manner as in Example 1 except that in the preparation of the coating liquid for an undercoat layer in Example 1, 33 parts of L-1571 (trade name, produced by Asahi Kasei Corporation, solids content 48%, Ig: 3° C.) was used in place of 63 parts of styrene-butadiene latex and 53 parts of modified starch (trade name: Petrocoat C-8, produced by Nippon Starch Chemical Co., Ltd., solids content: 30%) was added.

Example 6

[0068] A heat-sensitive recording material was obtained in the same manner as in Example 1 except that in the preparation of the coating liquid for an undercoat layer in Example 1, 200 parts of hollow particles C (D50: 7.5 μm, solids content: 10.0%) was used in place of 154 parts of hollow particles A. The proportion of hollow plastic particles having an average particle diameter of 5.0 μm or more in the undercoat layer was 20 mass %.

Example 7

[0069] A heat-sensitive recording material was obtained in the same manner as in Example 1 except that in the preparation of the coating liquid for an undercoat layer in Example 1, 485 parts of hollow plastic particles D (trade name: Matsumoto Microsphere F series, produced by Matsumoto Yushi Co., Ltd., D50: 3.5 μm, solids content: 13.0%) were used in place of 154 parts of hollow plastic particles A and the amount of hollow plastic particles B used was changed to 0 parts from 162 parts.

Comparative Example 1

[0070] A heat-sensitive recording material was obtained in the same manner as in Example 1 except that in the preparation of the coating liquid for an undercoat layer in Example 1, 154 parts of hollow plastic particles D (trade name: Matsumoto Microsphere F series, produced by Matsumoto Yushi Co., Ltd., D50: 3.5 μm, solids content: 13.0%) were used in place of hollow plastic particles A.

Comparative Example 2

[0071] A heat-sensitive recording material was obtained in the same manner as in Example 1 except that in the preparation of the coating liquid for an undercoat layer in Example 1, the amount of hollow plastic particles A used was changed to 0 parts from 154 parts, and 238 parts of hollow plastic particles B were used in place of 162 parts thereof.

[0072] The heat-sensitive recording materials prepared in Examples 1 to 7 and Comparative Examples 1 and 2 above were subjected to the following evaluations. Table 1 shows the results.

Elastic Modulus (Nanoindentation Method)

[0073] The elastic modulus (unit: N/mm.sup.2) was measured under a load of 0.7 mN (indenter: a spherical indenter with ϕ100 μm, no spring correction, holding time: 1000 msec, number of divisions: 500, step interval: 30 msec, Poisson's ratio: fused quartz: 0.17) using an ENT-2100 nanoindentation system produced by Elionix Inc.

Medium Energy Development Density

[0074] An image was recorded on each heat-sensitive recording material at an applied energy of 0.16 mJ/dot in a medium energy range using a thermal recording tester (trade name: TH-PMD, produced by Ohkura Electric Co., Ltd.). The obtained printed portion was measured with a Macbeth densitometer (trade name: RD-914, produced by Macbeth Co., Ltd.) in visual mode. A greater numerical value indicates a higher print density. The recording density is preferably 0.90 or more for practical use.

Saturated Recording Density

[0075] An image was recorded on each heat-sensitive recording material at an applied energy of 0.24 mJ/dot in a high energy region using a thermal recording tester (trade name: TH-PMD, produced by Ohkura Electric Co., Ltd.). The Obtained printed portion was measured with a Macbeth densitometer (trade name: RD-914, produced by Macbeth Co., Ltd.) in visual mode. A greater numerical value indicates a higher print density. The recording density is preferably 1.30 or more for practical use.

Image Quality

[0076] A barcode was recorded using a label printer (trade name: L-2000, produced by Ishida Co., Ltd.). The recorded image quality was visually observed and evaluated according to the following criteria: [0077] A: Almost no image defects are observed, and the recording density is uniform. [0078] B: Image defects are slightly observed. [0079] C: Image defects are observed, and the print density is not uniform, but is practically acceptable. [0080] D: Many image defects are observed, and are problematic is actual use.

TABLE-US-00001 TABLE 1 Elastic Recording density Image modulus 0.16 mJ/dot 0.24 mJ/dot quality Example 1 124 0.15 1.38 A Example 2 98 1.18 1.21 A Example 3 142 1.10 1.39 B Example 4 155 1.05 1.37 B Example 5 180 0.99 1.36 C Example 6 132 1.21 1.39 A Example 7 141 0.81 1.32 C Camp. Ex. 1 312 0.74 1.34 D Comp. Ex. 2 468 0.62 1.35 D