JPH0414078B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a thermal recording medium, and more particularly to a thermal recording medium that prevents a recorded image from decoloring. A thermal recording medium is a device that obtains images by utilizing physical and scientific changes in substances caused by thermal energy, and a large number of processes are being studied. Recently, thermosensitive recording materials have come to be used as output recording paper for facsimiles and computers, taking advantage of their characteristics such as primary color development and no need for a developing process. These are called dye types, and include, for example, U.S. Patent No. 3539375, Japanese Patent Publication No. 4160-43, and Japanese Patent Publication No. 45-45.
No. 14039, Japanese Patent Application Laid-Open No. 55-27253, etc. In general, when a thermosensitive recording medium is used as recording paper, it has the advantage that the recording apparatus can be made lighter and smaller, and its use has rapidly come into use in recent years. On the other hand, a drawback of thermosensitive recording materials is that the resulting recorded images are subject to significant discoloration, particularly when stored in high temperature and high humidity environments or when exposed to light. Various methods have been proposed for the purpose of improving the above-mentioned drawbacks of heat-sensitive recording materials. For example, Special Publication No. 51-43386, Special Publication No. 54-12820
No. 58-87089 and JP-A-58-87089 disclose the addition of various phenolic antioxidants, and JP-A-53-17346.
JP-A-53-17347 and JP-A-55-34901 disclose the addition of various resins;
No. 72996 describes the addition of terephthalic acid ester. However, these methods have the drawback that the effect of preventing color fading is not sufficient and that unnecessary color development, so-called "fogging" occurs during the production of the recording medium or during storage of the recording medium. Further, new problems such as staking and adhesion of residue to the heat-sensitive head arise. As a result of intensive studies to solve these problems, the inventors of the present invention found that a heat-sensitive recording material containing a colorless or light-colored electron-donating dye, a phenolic compound, and a specific hindered amine compound derived from butanetetracarboxylic acid. The present inventors have discovered that this method does not cause fogging, has little discoloration of recorded images due to humidity and heat, and does not cause problems such as adhesion of residue, and has arrived at the present invention. The electron-donating dye used in the present invention is not particularly limited as long as it is used in general pressure-sensitive recording paper, heat-sensitive recording paper, etc. Specific examples include (1) triarylmethane compounds such as 3,3-
Bis(p-dimethylaminophenyl)-6-dimethylaminophthalide (crystal violet lactone), 3-(p-dimethylaminophenyl)-3-(1,2-dimethylindol-3-yl)phthalide , 3-(p-dimethylaminophenyl)-3-(2-phenylindol-3-yl)
phthalide, 3,3-bis-(8-ethylcarbazol-3-yl)-3-dimethylaminophthalide,
3,3-bis-(2-phenylindole-3-
yl)-5-dimethylaminophthalide, etc.: (2) Diphenylmethane compounds, such as 4,4'-bis-
Dimethylaminobenzhydrin benzyl ether, N-halophenyl leukoolamine, N-
2,4,5-trichlorophenylleukoolamine, etc.: (3) Xanthene compounds, such as rhodamine B-anilinolactam, 3-diethylamino-
7-dibenzylaminofluorane, 3-diethylamino-7-octylaminofluorane, 3-diethylamino-7-(2-chloroanilinofluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3 -diethylamino-6-chloro-7-(β-ethoxyethyl)aminofluorane, 3-biperidino-6-methyl-7-anilinofluorane, 3-ethyl-tolylamino-6-
Methyl-7-anilinofluorane, 3-cyclohexylmethylanilino-6-methyl-7-anilinofluorane, 3-diethylamino-6-chloro-7-β-ethoxyethylaminofluorane, 3
-diethylamino-6-chloro-7-γ-chloropropylaminofluorane, etc.: (4) Thiazine compounds, such as benzoylleucomethylene blue,
p-Nitrobenzoylleucomethylene blue, etc.:
(5) Spiro compounds, such as 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3-benzylspiro-dinaphthopyran, 3-methylnaphtho-(3-methoxy-benzo)
-spiropyran, etc., or a mixture thereof. These are determined by the application and desired properties. Specifically, the phenolic compounds used in the present invention include p-octylphenol, p-
tert-butylphenol, p-phenylphenol, 1,1-bis(p-hydroxyphenyl)propane, 2,2-bis(p-hydroxyphenyl)propane, 1,1-bis(p-hydroxyphenyl) ) pentane, 1,1-bis(p-hydroxyphenyl)hexane, 2,2-bis(p-hydroxyphenyl)hexane, 1,1-bis(p-
hydroxyphenyl)-2-ethyl-hexane,
2,2-bis(4-hydroxy-3,5-dichlorophenyl)propane, p-hydroxybenzoic acid, ethyl p-hydroxybenzoate, butyl p-hydroxybenzoate, 3,5-di-tert-butylsalicylic acid , 3,5-di-α-methylbenzylsalicylic acid, propyl p-hydroxybenzoate, p
-isopropyl p-hydroxybenzoate, isobutyl p-hydroxybenzoate, heptyl p-hydroxybenzoate, benzyl p-hydroxybenzoate,
p-hydroxydiphenoxide, α-naphthol, β-naphthol, p-hydroxyacetonephenone, p-t-octylcatechol, bis(o
-hydroxyphenyl), bis(o-hydroxy-p-chlorophenyl)methane, 2,2-bis(p-hydroxyphenyl)butane, 2,2-bis(m-methyl-p-hydroxyphenyl)propane, 2,2-bis(m,m'-dimethyl-p-
Examples include hydroxyphenyl) propane. The hindered amine compound used in the present invention is a compound derived from butanetetracarboxylic acid and represented by the following general formula. (In the formula, R ₁ represents a hydrogen atom or a methyl group,
R ₂ and R ₃ are each independently

[Formula] or represents an alkyl group, R ₄ is

[Formula] Alkyl group or shows. ) Specific examples of the compound represented by the above general formula include those shown below. No.1 Tetra (2,2,6,6-tetramethyl-
4-Piperidyl)-1,2,3,4-butanetetracarboxylate, No.2 Tris(2,2,6,6-tetramethyl-
4-piperidyl) mono(isotridecyl)-
1,2,3,4-butanetetracarboxylate, No. 3 Tetra(1,2,2,6,6-pentamethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate, No. 4 Tris(1,2,2,6,6-pentamethyl-4-piperidyl) mono(isotridecyl)-1,2,3,4-butanetetracarboxylate, No.5 Bis(1,2,2,6 , 6-pentamethyl-4-piperidyl) di(tridecyl)-1,
2,3,4-butanetetracarboxylate, No.6 bis(2,2,6,6-tetramethyl-4
-piperidyl) di(tridecyl)-1,2,
3,4-butanetetracarboxylate, No. 7 3,9-bis[1,1-dimethyl-2-
{Tris(2,2,6,6-tetramethyl-
4-Piperidyloxycarbonyl)butylcarbonyloxy}ethyl]-2,4,8,10
-Tetraoxaspiro[5,5]undecane, No.8 3,9-bis[1,1-dimethyl-2-
{tris(1,2,2,6,6-pentamethyl-4-piperidyloxycarbonyl)butylcarbonyloxy}ethyl]-2,4,8,
10-Tetraoxaspiro[5,5]undecane. In the present invention, it is preferable to use a hindered phenol compound in combination. A specific example of a hindered phenol compound is 1,1,3-tris(2
-Methyl-4-hydroxy-5-t-butylphenyl)butane, 2,2'-methylenebis(4-methyl-6-t-butylphenol), 2,2'-methylenebis(4,6-di-t-butyl) phenol),
2,2'-ethylidene bis(4,6-di-t-butylphenol), 2,2'-ethylidene bis(4-
sec-butyl-6-t-butylphenol), 2,
2'-methylenebis(4-ethyl-6-butylphenol), 4,4'-methylenebis(2-methyl-
6-t-butylphenol), 4,4'-methylenebis(2,6-di-t-butylphenol), 2,
2'-methylenebis(4-methyl-6-α-methylcyclohexylphenol), 4,4'-butylidenebis(3-methyl-6-t-butylphenol), 2,2'-thiobis(4-methyl-6- t-
butylphenol), 2,2'-thiobis(4,6
-di-t-butylphenol), 4,4'-thiobis(3-methyl-6-t-butylphenol),
Examples include 4,4'-thiobis(2-methyl-6-t-butylphenol). When producing a coating liquid for heat-sensitive recording material, it is necessary to disperse the above-mentioned material for heat-sensitive recording material using water as a dispersion medium. At this time, it is preferable to use water-soluble polymers such as polyvinyl alcohol, hydroxyethyl cellulose, and starch derivatives. A method for dispersing materials for heat-sensitive recording materials using these dispersion media generally involves using a dispersion medium containing a water-soluble polymer in an amount of 1% to 10% by weight, more preferably 2% to 5% by weight. An electron-donating dye, phenolic compound, or hindered amine compound is added from 10% by weight to 50% by weight, and dispersed using a dispersing machine such as a ball mill, sand mill, attritor, or colloid mill. To the mixture of the above dispersion liquid, oil-absorbing pigments, waxes, metal soaps, etc. are further added as necessary to make a coating liquid for heat-sensitive recording material, and the coating liquid is applied onto a support such as paper or plastic to achieve the desired effect. Obtain a thermosensitive recording medium. Oil-absorbing pigments include kaolin, calcined kaolin, talc, waxite, diatomaceous earth, calcium carbonate, aluminum hydroxide, magnesium hydroxide,
Magnesium carbonate, titanium oxide, barium carbonate,
Selected from urea-formalin filler, cellulose filler, etc. Examples of waxes include paraffin wax, cownabar wax, microcrystalline wax, polyethylene wax, and higher fatty acid amides such as stearic acid amide, ethylene bisstearamide, and higher fatty acid esters. Examples of metal soaps include higher fatty acid polyvalent metal salts such as zinc stearate, aluminum stearate, calcium stearate, and zinc oleate. Examples will be shown below, but the present invention is not limited thereto. Example 1 20 g of 3-diethylamino-6-chloro-7-anilinofluorane was dispersed overnight in a 300 ml ball mill with 100 g of a 10% polyvinyl alcohol (saponification degree 98%, polymerization degree 500) aqueous solution to obtain dispersion A. . Similarly, add 20g of benzyl p-hydroxybenzoate.
With 100g of 10% polyvinyl alcohol aqueous solution
Dispersion B was obtained by dispersing in a 300 ml ball mill overnight. Similarly, 10 g of No. 1 hindered amine compound
%300 with 100g of polyvinyl alcohol aqueous solution
Dispersion C was obtained by dispersing the mixture in a ml ball mill for one day. Dispersion A, Dispersion B and Dispersion C at 3:10:5
Mix at a weight ratio of 200g of the mixed liquid,
50 g of calcium carbonate fine powder was added and sufficiently dispersed to form a coating liquid. This coating liquid for heat-sensitive recording material was applied onto a base paper having a basis weight of 50 g/m ² to obtain a coating amount of 6 g/m ² in terms of solid content, and dried at 50° C. for 2 minutes to obtain a heat-sensitive recording material. . Example 2 Benzyl p-hydroxybenzoate 20 of Example 1
A heat-sensitive recording material was obtained in the same manner as in Example 1, except that 20 g of 2,2-bis-(p-hydroxyphenyl)propane was used instead of 2,2-bis-(p-hydroxyphenyl)propane to obtain dispersion B. Examples 3 to 5 20 g of No. 1 hindered amine compound of Example 1
A heat-sensitive recording material was obtained in the same manner as in Example 1, except that 20 g of the following hindered amine compound was used instead of Dispersion C. Example Hindered amine compound 3 No. 4 4 No. 6 5 No. 8 Comparative example 1 20 g of hindered amine compound No. 1 of Example 1
1,1,3-tris(2-methyl-4-
Hydroxy-5-t-butylphenyl)butane 20
A thermosensitive recording material was obtained in the same manner as in Example 1, except that dispersion C was obtained using the following. Example 6 20 g of No. 1 hindered amine compound of Example 1
A thermosensitive recording material was prepared in the same manner as in Example 1, except that 10 g of the mixture was replaced with 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane to obtain dispersion C. Obtained. <Comparative Test> A comparative test of the heat-sensitive recording bodies obtained in the above Examples and Comparative Examples was conducted as follows. 1 High temperature and high humidity storage test Commercially available heat-sensitive facsimile machine NEFAX-3000
(manufactured by NEC Corporation), stored for 24 hours under two conditions: temperature 50°C humidity 90% and temperature 70°C dry state.
The density of the skin of the sample after storage was measured. Separately, the density of the printed area of the sample before and after storage was measured, and the residual rate of the density of the printed area after storage was determined from the following formula. Remaining rate (%) = Concentration after storage / Concentration before storage × 100 2. Light resistance storage test After printing with NEFAX-3000, the sample was exposed to sunlight for 10 days, and the skin density of the sample after exposure was measured. Separately, measure the density of the printed part of the sample before and after exposure,
The residual rate of printed area density was determined in the same manner as the storage test. 3 States King Test Printing was performed using NEFAX-3000 in an atmosphere of 0°C, and the presence or absence of states king was examined. 4. Scum adhesion test 3m solid printing was performed using NEFAX-3000 in an atmosphere of 20°C, and dirt around the thermal head was visually determined. Table 1 shows the results of the above tests. All color density measurements are made using a Macbeth densitometer.
This was done using the RD-514 model.

【table】

Claims (1)

[Scope of Claims] 1. A heat-sensitive recording material comprising a colorless or light-colored electron-donating dye, a phenolic compound, and a hindered amine compound represented by the following general formula. (In the formula, R ₁ represents a hydrogen atom or a methyl group,
R ₂ and R ₃ each independently represent [Formula] or an alkyl group, and R ₄ represents [Formula] an alkyl group or shows. )