JPH06255263A - Thermal recording material - Google Patents

Abstract

PURPOSE:To provide a thermal recording material provided with a heat-sensitive layer having a superior resistance to solvents in an unprinted part, superior resistance to oils and resistance to plasticizer in an image part, and a high transparency by incorporating a compound shown by a specific formula in a color developer. CONSTITUTION:A thermal recording material is provided with a sheet substrate and a thermally color-forming layer containing a dye precursor and a color developer. The color developer contains at least one kind of compound shown by formula I. In formula I, R<1> is one member selected out o an aromatic group having no substituent or aromatic group substituted by at least one member selected out of alkyl, aryl, aralkyl, alkyloxy, acyl, alkyloxycarbonyl, aryloxycarbonyl, halogen atom, cyano, and nitro, and R<2>, R<3> are one member independently selected out of hydrogen atom, alkyl, alkyloxy, acyl, alkyloxycarbonyl, halogen atom, cyano, and nitro.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive recording material for forming a color image by heating. More specifically, the present invention relates to a heat-sensitive recording material suitable for a recording sheet which is excellent in solvent resistance of a white background portion, oil resistance of an image portion, and plasticizer resistance, and which further requires transparency in a heat-sensitive layer. Is. Such thermal recording materials include recording sheets for overhead projectors, cash dispenser paper, ticket, commuter pass, POS label, prepaid card, air tag, betting ticket paper, CRT medical measuring instrument, scientific measuring instrument printer paper. It is suitable for applications such as.

[0002]

2. Description of the Related Art A heat-sensitive recording material is generally composed of a support such as paper, synthetic paper or plastic film on which a color-forming substance such as an electron-donating leuco dye and an organic acid such as an electron-accepting phenolic compound. A heat-sensitive layer containing a color-developing substance such as a substance as a main component is provided, and a recorded image can be formed by reacting these color-forming components with thermal energy. Such a thermal recording material is disclosed in, for example, Japanese Patent Publication No.
It is disclosed in Japanese Patent Publication No. 3-4160, Japanese Patent Publication No. 45-14039, Japanese Patent Publication No. 48-27736, etc., and has been widely put into practical use.

These thermosensitive recording media are used for the output of electronic calculators, facsimiles, automatic ticket vending machines, printers of scientific measuring instruments, or CRT medical measuring instruments because the recording device is compact, inexpensive and easy to maintain. Widely used in printers, etc. With the expansion of the application range of such a thermal recording material, the thermal recording material may come into contact with a cosmetic cream, solvent, oil, or a polymer sheet containing a plasticizer, or under severe conditions such as high temperature and high humidity. The opportunity to be placed in has increased. However, a conventional so-called dye-type thermosensitive recording medium formed by coating a thermosensitive coloring layer containing a color-forming dye substance, a color-developing substance, and a binder as an active ingredient on a support has a white background. When a solvent comes into contact with the product, or when oil or a plasticizer comes into contact with the image area,
It had a defect that the color was rapidly erased.

As a method for solving this drawback, Japanese Unexamined Patent Publication No. Sho.
6-146795 and JP-A-58-199189.
As shown in No. 6, a method of providing a protective layer on the heat-sensitive layer has been proposed, but it is ineffective for contacting solvents, oils, and plasticizers from the back and end faces, and it can be said that this is an essential solution. Absent.

On the other hand, in a thermosensitive recording medium, usually a color-forming substance and a color-developing substance are separately dispersed in the form of fine particles, which are then mixed with a binder, a pigment and other additives to prepare a mixed coating solution. Is coated and dried on a support to form a thermosensitive coloring layer, but the thermosensitive coloring layer obtained by this method is poor in transparency, and therefore, to be applied to a recording sheet for an overhead projector. , Its transparency was insufficient.

In addition, when it is applied to cash dispenser papers, tickets, commuter passes, POS labels, prepaid cards, air bills, betting ticket papers, CRT medical measuring instruments, printers for scientific measuring instruments, etc., which are often printed. However, there is a problem in that when the thermosensitive coloring layer is formed on a substrate which has been printed in advance, the printed surface is hidden. In this case, printing is performed on the thermosensitive coloring layer, but printing on the thermosensitive coloring layer is often not easy, and it is necessary to overcoat with polyvinyl alcohol or the like in order to improve printability.

As a method for solving these drawbacks, the constituent components of the thermosensitive coloring layer are limited to color-forming substances, color-developing substances, dispersants, and binders (JP-A-63-236683).
No.) and a color-forming substance are microencapsulated, and the color-developing substance is emulsified and dispersed by a specific method (JP-A-63-26).
No. 5682) methods have been proposed, but they have drawbacks such as limited application range or complicated manufacturing method.

Generally, in order to impart transparency to the thermosensitive color developing layer, a method of dissolving a color forming substance, a color developing substance and a binder and other additives in a solvent, coating and drying on a support, a so-called solvent Although it is considered that coating is effective, this method is used because a general organic acidic developer and a color-forming substance cause a color-developing reaction promptly by making contact at the molecular level in a solvent. could not.

[0009]

SUMMARY OF THE INVENTION The present invention solves the above problems and prevents the white background from being colored by contact with a solvent and the image area from being discolored by contact with oil or a plasticizer. Highly transparent thermosensitive coloring layer, including recording sheets for overhead projectors, cash dispenser paper, ticket, commuter pass, POS label, prepaid card, air ticket, betting ticket paper, CRT medical measuring instrument, scientific measuring instrument The present invention intends to provide a heat-sensitive recording material suitable for use in printer paper and the like.

[0010]

DISCLOSURE OF THE INVENTION The inventors of the present invention have diligently studied a solvent-applicable thermosensitive coloring composition which is excellent in solvent resistance in a white background, oil resistance in an image area, and plasticizer resistance. As a result, they have found that a desired thermosensitive color-forming composition can be obtained by using a compound having a cyclohexyl aryl sulfonate as a specific chemical structure as a developer, and completed the present invention.

The thermosensitive recording medium of the present invention comprises a sheet-shaped substrate,
A thermosensitive coloring layer formed on at least one surface of the sheet-like substrate and containing a substantially colorless dye precursor, and a color developer that reacts with the dye precursor under heating to develop a color thereof; The developer has the following general formula (1):

[Chemical 2] [Wherein R ¹ is an aromatic group having no substituent, and an alkyl group, an aryl group, an aralkyl group, an alkyloxy group, an acyl group, an alkyloxycarbonyl group, an aryloxycarbonyl group, a halogen atom, a cyano group. , And a member selected from an aromatic group substituted by at least one member selected from a nitro group, R ² , R
³ are each independently a hydrogen atom, an alkyl group,
It represents a member selected from an alkyloxy group, an acyl group, an alkyloxycarbonyl group, a halogen atom, a cyano group, and a nitro group. ] It is characterized by containing at least 1 sort (s) of compound represented by these.

[0012]

The sulfonic acid ester having a specific chemical structure, an arylsulfonic acid cyclohexyl skeleton, used in the present invention hardly causes a color-forming reaction at room temperature even when it comes into contact with an electron-donating dye at a molecular level. Therefore, when the above compound and a color former, a binder and other additives are dissolved in a solvent and coated on a support and dried, a substantially colorless and transparent thermosensitive color forming layer is formed. Further, even if a solvent is dropped on the heat-sensitive color developing layer, no color developing reaction occurs. However, this heat-sensitive recording material has an excellent performance in that when it is heated, a color-developing reaction occurs promptly, and even when oil or a plasticizer is applied to the obtained color-developed image, decolorization hardly occurs. It is a thing.

Although the details of the mechanism of this unique color development reaction are unknown, it is speculated that the developer of the present invention produces sulfonic acid by heating. That is, the color developing agent of the present invention does not exhibit color developing ability because it does not have an acidic group before heating, and therefore, solvent coating is possible, and the thermosensitive coloring layer is in contact with a solvent. Does not develop color. However, when sulfonic acid is produced by heating, it immediately reacts with the color former to form a color image. The details of the reason why the obtained color image has high oil resistance and plasticizer resistance are not clear, but it is presumed that the high acidity of the sulfonic acid has an effect.

Examples of the sulfonic acid ester of the general formula (1) used in the present invention include the following compounds.

[0015]

[Chemical 3]

[0016]

[Chemical 4]

[0017]

[Chemical 5]

[0018]

[Chemical 6]

[0019]

[Chemical 7]

These compounds may be used alone or in combination of two or more.

The sulfonic acid esters of the general formula (1) are
It can be synthesized by using the corresponding sulfonic acid chloride and cyclohexanol as raw materials and adding and reacting pyridine as a base. However, the method for synthesizing the developer of formula (1) of the present invention is not limited to the above method.

The leuco dye used as the dye precursor in the present invention can be selected from conventionally known ones such as triphenylmethane type, fluorane type and diphenylmethane type compounds. Such leuco dyes are, for example,
3- (4-diethylamino-2-ethoxyphenyl)-
3- (1-ethyl-2-methylindol-3-yl)
-4-azaphthalide, crystal violet lactone, 3- (N-ethyl-N-isopentylamino) -6
-Methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7- (o, p-dimethylanilino) fluorane, 3- (N -Ethyl-N-p-toluidino) -6-methyl-7-anilinofluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3-dibutylamino-6-methyl-7-anilinofluor Oran,
3- (N-cyclohexyl-N-methylamino) -6-
Methyl-7-anilinofluorane, 3-diethylamino-7- (o-chloroanilino) fluorane, 3-diethylamino-7- (m-trifluoromethylanilino) fluorane, 3-diethylamino-6-methyl-7-chloro Fluorane, 3-diethylamino-6-methylfluorane, and 3-cyclohexylamino-6-chlorofluorane, 3- (N-ethyl-N-hexylamino)-
One or more selected from 6-methyl-7- (p-chloroanilino) fluorane and the like can be used.

Further, in the present invention, a heat-fusible substance (so-called sensitizer) may be used in combination in the heat-sensitive color forming layer within a range that does not impair the desired effect. As the sensitizer, a heat-fusible organic compound having a melting point of 50 to 150 ° C. is used, and examples thereof include 1-hydroxy-2-naphthoic acid phenyl ester (Japanese Patent Laid-Open No. 1991089/1982) and p-benzylbiphenyl. (JP-A-60-82382), benzylnaphthyl ether (JP-A-58-87094), dibenzyl terephthalate (JP-A-58-98285).
No.), benzyl p-benzyloxybenzoate (Japanese Patent Application Laid-Open No. 5 (1999) -58242).
7-201691), diphenyl carbonate, ditolyl carbonate (JP-A-58-136489), m-terphenyl (JP-A-57-89994), 1,2-bis (m-tolyloxy) ethane (JP-A-SHO). 60-56588),
1,5-bis (p-methoxyphenoxy) -3-oxapentane (JP-A-62-181183), oxalic acid diester (JP-A-64-1583), and 1,4-
Bis (p-tolyloxy) benzene (JP-A-2-153
No. 783) and the like.

The heat-sensitive color developing layer of the present invention may contain a hindered phenol compound or an ultraviolet absorber for the purpose of improving the storage stability of a color image. They are disclosed, for example, in JP-A-57-151394 and JP-A-58-1601.
91, JP-A-58-69096, JP-A-59-28.
84, JP-A-59-95190, JP-A-60-22.
288, JP-A-60-255485, and JP-A-61-161.
44686, JP-A-62-169683, JP-A-6
3-17081, JP-A-1-249385, JP-A-4-144786, and the like. Specifically, for example, 1,1,3-tris (3'-cyclohexyl- 4'-hydroxyphenyl)
Butane, 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 4,
4'-thiobis (3-methyl-6-tert-butylphenol) 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) benzene, 2, 2'-dihydroxy-4,4 '
-Dimethoxybenzophenone, p-octylphenyl salicylate, 2- (2'-hydroxy-5'-methylphenyl) benzotriazole, ethyl-2-cyano-
3,3'-diphenyl acrylate, and tetra (2,2,6,6, -tetramethyl-4-piperidyl)
1,2,3,4-butane tetracarboate and the like.

Further, the thermosensitive color developing layer of the present invention may contain a compound having an aziridinyl group or an epoxy group for the purpose of improving the storage stability of a color image. . Examples of compounds having an aziridinyl group used in the present invention include:
Although described in JP-A-4-113888, the following compounds can be specifically mentioned.

That is, 2,4-bis (1-aziridinylcarbonylamino) toluene, bis (4- (1-aziridinylcarbonylamino) phenyl) methane, bis (3-chloro-4- (1-azide) Lysinylcarbonylamino) phenyl) methane, 2,2-bis (4- (1-aziridinylcarbonyloxy) phenyl) propane, 1,
4-bis (1-aziridinylcarbonyloxy) benzene, 1,4-bis (1-aziridinylcarbonyl) benzene and the like.

Examples of the compound having an epoxy group used in the present invention include bis (4-glycidyloxyphenyl) sulfone and bis (4-glycidyloxyphenyl).
Examples thereof include sulfide, (4-glycidyloxyphenyl) phenyl sulfone, bis (4-glycidyloxyphenyl) amine, and bis (4-glycidyloxyphenyl) ether.

The heat-sensitive recording material of the present invention may have a protective layer for the purpose of improving the storage stability of the color image. Examples of the polymer used in this protective layer include methyl cellulose, carboxymethyl cellulose, hydroxymethyl cellulose, gelatin, casein, modified starch, polyvinyl alcohol, polyvinyl pyrrolidone, acrylic ester copolymer, acrylic compound-styrene copolymer, maleic acid modified acrylic. Examples include acids.

Examples of the binder used in the thermosensitive coloring layer of the present invention include polyvinyl acetate, polyurethane, styrene / budadiene copolymer, polyacrylic acid, polyacrylic acid ester, vinyl chloride / vinyl acetate copolymer. Examples thereof include polymer, polybutyl methacrylate, ethylene / vinyl acetate copolymer, acrylic copolymer, and styrene / butadiene / acrylic copolymer.

The heat-sensitive color forming layer of the heat-sensitive recording material of the present invention may contain waxes, organic or inorganic white pigments and the like, if necessary, within the range that does not impair the desired effect. As the wax, known waxes such as paraffin, amide wax, bisimide wax, and metal salt of superabsorbent fatty acid can be used.

Examples of organic or inorganic pigments include calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, clay, calcined clay, talc, and surface-treated calcium carbonate and silica. In addition to the above inorganic fine powder, organic fine powder such as urea-formalin resin, styrene / methacrylic acid copolymer, and polystyrene resin can be used.

Examples of the solvent used for preparing the coating liquid for the thermosensitive color developing layer include toluene, benzene, methyl ethyl ketone, methyl isobutyl ketone, acetone, ethyl acetate, butyl acetate and tetrahydrofuran.

The content of the above leuco dye in the thermosensitive color developing layer is generally 5 to 20% by weight, and the content of the color developer is generally 5 to 40% by weight. When the sensitizer is contained, its content is preferably 10 to 40% by weight. When the hindered phenol compound or the ultraviolet absorber is contained, its content is preferably 1 to 10% by weight. When the aziridine compound or the epoxy compound is contained, its content is preferably 1 to 30% by weight. When waxes and white pigments are contained, the content of each is preferably 1 to 20% by weight and 1 to 30% by weight, and the content of the binder is generally 10 to 80% by weight.

The support used in the thermosensitive recording medium of the present invention is paper, coated paper whose surface is coated with a pigment, latex or the like, synthetic paper having a layered structure made of polyolefin resin, plastic film, or the like. You can choose from a composite sheet of.

To produce a thermosensitive recording medium, a coating solution containing a mixture of the above-mentioned required components is applied onto at least one surface of the above-mentioned sheet-like support and dried to form a thermosensitive coloring layer. The coating amount of the thermosensitive coloring layer is preferably ¹ to 15 g / m ² in the dried state of the coating liquid layer, and is ² to 10
g / m ² is particularly preferred.

[0036]

EXAMPLES The thermal recording material of the present invention will be further described with reference to the following examples. In the examples, "parts" and "%" represent "parts by weight" and "% by weight", respectively, unless otherwise specified.

Example 1 A thermosensitive recording sheet was prepared by the following procedure . 1) Preparation Ingredient Quantity of heat-sensitive coloring layer coating liquid (parts) 3- (N-ethyl--N--isopentylamino) - 1 6-methyl-7-anilinofluoran p- nitrobenzenesulfonate cyclohexyl (Formula Compound of 5) 2 Binder (acrylic copolymer, LR-347 (trademark), 5 Mitsubishi Rayon Co., Ltd.) Methyl ethyl ketone 70

2) Formation of thermosensitive coloring layer The above coating solution was applied to a polyester film (thickness: 50 μm).
Was coated and dried on a surface of No. 1 using a roll coater so that the coating amount after drying was 3 g / m ² , to form a thermosensitive color developing layer, thereby preparing a thermosensitive recording sheet.

3) Transparency test The transparency of the obtained thermosensitive recording sheet was visually evaluated. The evaluation results are shown in Table 1.

4) Color development test The obtained thermal recording sheet was heated for 5 seconds at a temperature of 120 ° C. and a pressure of 2.5 kg / cm ² using a tilt tester manufactured by Toyo Seiki. The color development state at this time was visually evaluated. The evaluation results are shown in Table 1.

5) Solvent resistance test of white background portion A small amount of acetone, ethanol or toluene was dropped on the obtained heat-sensitive recording sheet, and the presence or absence of each color was visually evaluated. The evaluation results are shown in Table 1.

6) Oil resistance and plasticizer resistance test of image area To the color developed image obtained in the above color development test, salad oil or dioctyl phthalate was applied using a cotton swab, and 30
The residual state of each image after the lapse of minutes was visually evaluated. The evaluation results are shown in Table 2.

Example 2 A thermal recording sheet was prepared in the same manner as in Example 1. However, in the preparation of the coating liquid, p-nitrobenzenesulfonic acid cyclohexyl (compound of formula 5) was used instead of p
-Cyclohexyl methoxybenzene sulfonate (Formula 6)
The compound) was used. The test results are shown in Tables 1 and 2.

Example 3 A thermal recording sheet was prepared in the same manner as in Example 1. However, in the preparation of the coating liquid, m instead of cyclohexyl p-nitrobenzenesulfonate (compound of formula 5) was used.
-Cyclohexyl nitrobenzene sulfonate (compound of formula 7) was used. The test results are shown in Tables 1 and 2.

Example 4 A thermal recording sheet was prepared in the same manner as in Example 1. However, in the preparation of the coating liquid, p-nitrobenzenesulfonic acid cyclohexyl (compound of formula 5) was used instead of p
-A cyclohexyl toluenesulfonate (compound of formula 3) was used. The test results are shown in Tables 1 and 2.

Example 5 A thermal recording sheet was prepared in the same manner as in Example 1. However, in the preparation of the coating liquid, cyclohexylbenzenesulfonate (compound of formula 2) was used instead of cyclohexyl p-nitrobenzenesulfonate (compound of formula 5). The test results are shown in Tables 1 and 2.

Example 6 A thermal recording sheet was prepared in the same manner as in Example 1. However, in the preparation of the coating liquid, instead of cyclohexyl p-nitrobenzenesulfonate (compound of formula 5),
Cyclohexyl 2,4,6-trimethylbenzenesulfonate (compound of formula 8) was used. The test results are shown in Tables 1 and 2.

Example 7 A thermal recording sheet was prepared in the same manner as in Example 1. However, in the preparation of the coating liquid, instead of cyclohexyl p-nitrobenzenesulfonate (compound of formula 5), 1
-Cyclohexyl naphthalene sulfonate (compound of formula 16) was used. The test results are shown in Tables 1 and 2.

Example 8 A thermal recording sheet was prepared in the same manner as in Example 1. However, in the preparation of the coating liquid, p-nitrobenzenesulfonic acid cyclohexyl (compound of formula 5) was used instead of p
-Toluenesulfonic acid (p-methylcyclohexyl)
(Compound of formula 10) was used. The test results are shown in Tables 1 and 2.

Comparative Example 1 A thermal recording sheet was prepared by the following procedure. 1) Preparation Ingredient Quantity of color former dispersion A (parts) 3- (N-ethyl--N--isopentylamino) - 20 6-methyl-7-anilinofluoran polyvinyl alcohol 10% solution 10 Water 70 The above composition The product was pulverized using a sand grinder at room temperature until the average particle size was 1 μm or less.

[0051] 2) The developer dispersion prepared Ingredient Quantity of B (parts) 2,2-bis (4-hydroxyphenyl) propane 20 polyvinyl alcohol 10% solution 10 Water 70 The composition using a sand grinder The powder was crushed at room temperature until the average particle diameter was 1 μm or less.

[0052] 3) a sensitizer dispersion prepared Ingredient Quantity of C (parts) of oxalic acid di-p-methylbenzyl ester 20 polyvinyl alcohol 10% solution 10 Water 70 The composition using a sand grinder, an average particle size It was crushed at room temperature until it became 1 μm or less.

4) Formation of Thermosensitive Coloring Layer A coating solution was prepared by mixing 100 parts of 10% modified polyvinyl alcohol aqueous solution with 60 parts of solution A, 120 parts of solution B and 120 parts of solution C. This coating solution was applied and dried on a polyester film by using a roll coater so that the coating amount after drying was 3 g / m ² , to form a thermosensitive color developing layer, thereby preparing a thermosensitive recording sheet.

The thermosensitive recording sheet obtained as described above was subjected to the same transparency test, color development test, solvent resistance test on white background, oil resistance and plasticizer resistance test on image area as in Example 1. did. The test results are shown in Tables 1 and 2.

Comparative Example 2 A thermal recording sheet was prepared in the same manner as in Comparative Example 1. However, in preparing the developer dispersion, 2,2-bis (4-
4-Hydroxy-4'-isopropoxydiphenyl sulfone was used instead of (hydroxyphenyl) propane. The test results are shown in Tables 1 and 2.

[0056]

[Table 1]

[0057]

[Table 2]

As is clear from Table 1, the heat-sensitive recording material of the present invention had good transparency and good color development by heating, and the white background thereof was excellent in solvent resistance. On the other hand, the heat-sensitive recording materials of Comparative Examples were good in color development by heating, but were inferior in transparency, and the white background portion was colored by contact with a solvent. Also,
As is clear from Table 2, the image area of the heat-sensitive recording material of the present invention is excellent in oil resistance and plasticizer resistance, but the heat-sensitive recording material of the comparative example has both oil resistance and plasticizer resistance. Was enough.

[0059]

The heat-sensitive recording material of the present invention contains a compound having a cyclohexyl skeleton having a specific chemical structure as a developer in the heat-sensitive layer, and thus can be produced by solvent coating and is obtained. The heat-sensitive color forming layer has high transparency, the white background is excellent in solvent resistance, and the color image area is excellent in oil resistance and plasticizer resistance.

Claims (1)

[Claims] 1. A sheet-like substrate, a dye precursor that is formed on at least one surface of the sheet-like substrate and is substantially colorless, and a developer that reacts with the dye precursor under heating to develop a color. A thermosensitive coloring layer containing an agent, wherein the color developer has the following general formula (1): [Wherein R ¹ is an aromatic group having no substituent, and an alkyl group, an aryl group, an aralkyl group, an alkyloxy group, an acyl group, an alkyloxycarbonyl group, an aryloxycarbonyl group, a halogen atom, a cyano group. , And a member selected from an aromatic group substituted by at least one member selected from a nitro group, R ² and R
Each ³ independently represents a member selected from a hydrogen atom, an alkyl group, an alkyloxy group, an acyl group, an alkyloxycarbonyl group, a halogen atom, a cyano group, and a nitro group. ] Represented by at least 1
A heat-sensitive recording material containing a compound of a kind.