JPH021037B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a heat-sensitive recording medium, and particularly to a heat-sensitive recording medium that is suitable for high-speed recording and that prevents recorded images from fading. Conventionally, heat-sensitive recording materials have been well known that utilize a color reaction between a colorless or light-colored basic dye and an organic or inorganic color-forming agent, and obtain a recorded image by bringing the two color-forming substances into contact with each other using heat. Recently, with remarkable progress in thermal recording methods, thermal faxes and thermal printers that use thermal heads have become faster, with thermal faxes recording speeds of 20 seconds for A4 size, and thermal printers recording speeds of over 120 characters/sec. is now possible. As the speed of the hardware field increases, the heat-sensitive recording media used must also have excellent recording sensitivity (dynamic recording characteristics), no static recording in the low temperature range (60 to 70 degrees Celsius), and the adhesion of dust. Characteristics such as the absence of recording gaps (piling) are required. As a conventionally known highly sensitive heat-sensitive recording medium, there is one in which a dye, a phenol compound such as bisphenol A, and a sensitizer such as stearic acid amide are combined. In such a highly sensitive heat-sensitive recording material, the recording layer usually contains a sensitizer and a phenol compound in a ratio of 2 to 5 parts dye to 1 part dye. However, as the recording sensitivity of such conventional heat-sensitive recording media improves, the temperature range (60 to 70
The disadvantage is that a so-called static record appears at temperatures (°C). Furthermore, since the amount of sensitizer is large, piling is also poor. Under these circumstances, there is currently a need for the development of a quality-balanced thermal recording medium suitable for high-speed recording. Therefore, in order to obtain a heat-sensitive recording medium suitable for high-speed recording hardware, the present inventors extensively investigated the field of coloring agents, and found that the use of hydroquinone monobenzyl ether is suitable for high-speed recording. I discovered that. Although it is not clear exactly why hydroquinone monobenzyl ether is suitable for high-speed recording, this substance itself has good crystallinity and exhibits sharp dissolution coloration. It is thought that the low melting point of around 120°C is the reason for the highly sensitive color development. Hydroquinone monobenzyl ether has such physical properties, so when it is used as a coloring agent for heat-sensitive recording media, a sensitizer is not required, and for this reason, the amount of melting during recording is This means that less amount is required, which is naturally effective in terms of piling. However, hydroquinone with these properties
Monobenzyl ether also exhibits thermochromic properties that exhibit color-forming and decolorizing reactions with dyes in relation to temperature, so it cannot be used as a color-forming agent for thermosensitive recording media immediately. There are some difficulties. Therefore, the present inventors have solved the decolorization of recorded images by combining hydroquinone monobenzyl ether with a colorless or light-colored basic dye, and have developed a thermosensitive recording medium that can exhibit the physical properties of this coloring agent. As a result of research on the development of the body, hydroquinone
It has been discovered that this object can be achieved by combining a monobenzyl ether and a colorless or light-colored basic dye with at least one compound represented by the following general formula [] or []. It was. [In the formula, R ₁ and R ₂ are each a C _1-8 alkyl group,
phenyl group

[Formula] or benzyl group

[Formula] is shown, and R ₃ and R ⁴ represent a hydrogen atom, a chlorine atom, a hydroxyl group, or a C _1-8 alkoxyl group. ] [In the formula, R ₅ , R ₆ and R ₇ each represent a hydrogen atom, a chlorine atom, a hydroxyl group, a C _1-12 alkoxyl group, a phenoxy group or a benzyloxy group. ] It is not clear why the thermochromic properties of hydroquinone/monobenzyl ether are eliminated when this compound is used in combination, but it is probably due to the melting and coloring reaction caused by heating, Therefore, recrystallization is thought to be the cause of discoloration, and it is thought that the combined use of the above compound may have the effect of inhibiting recrystallization. Various kinds of colorless or light-colored basic dyes are known to form the recording layer of the heat-sensitive recording medium according to the present invention, and the following are exemplified. 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, 3,3-bis(p-dimethylaminophenyl)phthalide, 3
-(p-dimethylaminophenyl))-3-(1,2
-dimethylindol-3-yl)phthalide, 3
-(p-dimethylaminophenyl)-3-(2-methylindol-3-yl)phthalide, 3,3-
Bis(1,2-dimethylindol-3-yl)
-5-dimethylaminophthalide, 3,3-bis(1,2-dimethylindol-3-yl)-6-
Dimethylaminophthalide, 3,3-bis(9-ethylcarbazol-3-yl)-6-dimethylaminophthalide, 3,3-bis(2-phenylindol-3-yl)-6-dimethylaminophthalide Do,
Triallylmethane dyes such as 3-p-dimethylaminophenyl-3-(1-methylpyrrol-3-yl)-6-dimethylaminophthalide, 4,4'-
Diphenylmethane dyes such as bis-dimemethylaminobenzhydryl benzyl ether, N-halophenyl-leucoauramine, N-2,4,5-trichlorophenylleucoauramine, benzoylleucomethylene blue, p-nitrobenzoylleucomethylene blue Thiazine dyes such as 3
-Methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3-phenyl-spiro-dinaphthopyran, 3-benzyl-spiro-dinaphthopyran, 3-methyl-naphtho(6'-methoxybenzo)sviropyran, 3-propyl-spiro - Spiro dyes such as dibenzopyran, lactam dyes such as rhodamine-B-anilinolactam, rhodamine (p-nitroanilino) lactam, rhodamine (o-chloroanilino) lactam, 3-dimethylamino-7-methoxyfluoran, 3 -diethylamino-6-methoxyfluorane, 3-diethylamino-7-methoxyfluorane, 3-diethylamino-7-chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-6,7 -dimethylfluorane, 3-(N-ethyl-p-toluidino)-7
-Methylfluorane, 3-diethylamino-7-
N-acetyl-N-methylaminofluorane, 3
-diethylamino-7-N-methylaminofluorane, 3-diethylamino-7-dibenzylaminofluorane, 3-diethylamino-7-N-methyl-N-benzylaminofluorane, 3-diethylamino-7-N-chloroethyl -N-methylaminofluorane, 3-diethylamino-7-N
-diethylaminofluorane, 3-(N-ethyl-p-toluidino)-6-methyl-7-phenylaminofluorane, 3-(N-ethyl-p-toluidino)-6-methyl-7-(p- toluidino)fluoran, 3-diethylamino-6-methyl-7
-phenylaminofluorane, 3-diethylamino-7-(2-carbomethoxy-phenylamino)
Fluoran, 3-(N-cyclohexyl-N-methylamino)-6-methyl-7-phenylaminofluoran, 3-pyrrolidino-6-methyl-7-
Phenylaminofluorane, 3-piperidino-6
-Methyl-7-phenylaminofluorane, 3-
Diethylamino-6-methyl-7-xylidinofluorane, 3-diethylamino-7-(o-chlorophenylamino)fluoran, 3-dibutylamino-7-(o-chlorophenylamino)fluoran, 3-pyrrolidino-6- Fluoran dyes such as methyl-7-p-butylphenylaminofluorane, etc. The heat-sensitive recording material of the present invention comprises a basic dye as described above, hydroquinone monobenzyl ether as a coloring agent, and a compound represented by the following general formula [] or []. [In the formula, R ₁ and R ₂ are each a C _1-8 alkyl group,
phenyl group

[Formula] or benzyl group

[Formula] is shown, and R ₃ and R ₄ represent a hydrogen atom, a chlorine atom, a hydroxyl group, or a C _1-8 alkoxyl group. ] [In the formula, R ₅ , R ₆ and R ₇ each represent a hydrogen atom, a chlorine atom, a hydroxyl group, a C _1-12 alkoxyl group, a phenoxy group or a benzyloxy group. ] Among the compounds represented by the general formula [] or [], compounds that are more preferably used are: , and compounds represented by the following general formula [] or []. [In the formula, R ₁₈ and R ₉ each represent a C _1-3 alkyl group. ) [In the formula, R ₁₀ is a hydroxyl group, a C _1-12 alkoxyl group, a phenoxy group, or a benzyloxy group, and R ₁₁
and _R12 each represent a hydrogen atom, a chlorine atom, a hydroxyl group, or a _C1-12 alkoxy group. ] Furthermore, among the compounds represented by the general formula [] or [], specifically exemplified are the compounds that are particularly preferably used: 4-hydroxydimethylphthalate mp.110℃ 4-hydroxydiethyltalate mp.65 ℃ 4-Hydroxydimethylisophthalate mp.98℃ 4-Hydroxydiethylisophthalate mp.55℃ 2,4-dihydroxybenzophenone mp.145℃ 2,4,4'-trihydroxybenzophenone
mp.200℃ 2,2',4,4'-tetrahydroxybenzophenone mp.195℃ 2-hydroxy-4-methoxybenzophenone
mp.65℃ 2-hydroxy-4-methoxy-4'-chlorobenzophenone mp.114℃ 2,2'-dihydroxy-4-methoxybenzophenone mp.70℃ 2,2'-dihydroxy-4,4 '-dimethoxybenzophenone mp.130℃ 2-hydroxy-4-n-octoxybenzophenone mp.49℃ 2-hydroxy-4-n-dodecyloxybenzophenone mp.52℃ 2-hydroxy-4- Examples include benzyloxybenzophenone mp.115℃. In the present invention, the proportion of hydroquinone monobenzyl ether blended into the recording layer is 100 to 700 parts by weight, preferably 150 to 400 parts by weight, per 100 parts by weight of the basic dye. Furthermore, at least one of the compounds represented by the general formula [], [], [] or []
Generally, 1 to 200 parts by weight, preferably 10 to 200 parts by weight of these compounds are blended per 100 parts by weight of hydroquinone monobenzyl ether. To prepare coating liquids containing these basic dyes, hydroquinone monobenzyl ether, and the compound represented by the above general formula, water is generally used as a dispersion medium, and dyes, dyes, etc. It is prepared as a coating liquid by dispersing colorants, etc. Such coating liquids usually contain starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, gum arabic, polyvinyl alcohol, styrene/maleic anhydride copolymer salt, styrene/acrylic acid copolymer temperature, and styrene as binders.・Butadiene copolymer emulsion etc. has a total solid content of 10
It is used in an amount of 40 to 40% by weight, preferably 15 to 30% by weight. Furthermore, various auxiliary agents can be added to the coating liquid. For example, sodium dioctyl sulfosuccinate, sodium dodecylbenzenesulfonate,
Dispersants such as lauryl alcohol sulfate/sodium salt, fatty acid metal salts, ultraviolet absorbers such as triazoles, other antifoaming agents, fluorescent dyes,
Examples include colored dyes. In addition, stearic acid, polyethylene, carnauba wax, paraffin wax, zinc stearate, calcium stearate, ester wax, etc. are dispersed in the paint to prevent state kinging when the heat-sensitive recording material comes into contact with recording equipment or recording heads. A liquid or emulsion can also be added. Inorganic pigments such as kaolin, clay, talc, calcium carbonate, calcined clay, titanium oxide, diatomaceous earth, fine particulate anhydrous silica, and activated clay may be added to improve the adhesion of residue to the recording head. In addition, stearic acid amide, stearic acid methylene bisamide, oleic acid amide,
Palmitic acid amide, matcha oleic acid amide, coconut fatty acid amide, etc. can also be added as a sensitizer. Furthermore, common coloring agents such as phenols can also be added within a range that does not impede the effects of the present invention. Supports include paper, plastic film,
Synthetic paper and the like can be used, but paper is most preferably used in terms of cost, applicability, etc. Further, the amount of coating liquid forming the recording layer applied to the support is not particularly limited, but is usually 2 to 12 g/m ² in terms of dry weight,
Preferably it is in the range of 3 to 10 g/m ² . The heat-sensitive recording material of the present invention thus obtained has suitability for high-speed recording, can eliminate the tendency of recorded images to fade even when the temperature decreases, and has excellent properties in terms of dust adhesion to the recording needle (piling). have. The present invention will be described in more detail with reference to Examples below, but it is of course not limited thereto. Further, unless otherwise specified, parts and percentages in the examples indicate parts by weight and percentages by weight, respectively. Example 1 Preparation of Solution A 3-(N-cyclohexyl-N-methylamino)-6-methyl-7-phenylaminofluorane 10 parts Methyl cellulose 5% aqueous solution 20 parts Water 10 parts This composition was mixed with sand grinding goo. It was pulverized until the average particle size was 3 μm. Preparation of Solution B Hydroquinone monobenzyl ether 20 parts 4-hydroxydimethyl phthalate 15 parts Methyl cellulose 5% aqueous solution 70 parts Water 30 parts This composition was ground with a sand glider until the average particle size was 3 μm. Formation of recording layer 40 parts of liquid A, 135 parts of liquid B, 30 parts of silicon oxide pigment (oil absorption 180ml/100g), 20% oxidized starch aqueous solution
Mix 100 parts and 70 parts of water and stir. The obtained coating liquid was applied to 50 g/m ² base paper with a coating weight of 7 g/m ² after drying.
A heat-sensitive recording paper was obtained by coating and drying so as to obtain the following. Example 2 Preparation of Solution A 3-(N-Ethyl-p-toluidino-6-methyl-7-phenylaminofluorane 10 parts Methyl cellulose 5% aqueous solution 20 parts Water 10 parts This composition was mixed with a sand glider to determine the average particle size. The average particle size of this composition was pulverized using a sand glider. Grinded to 3 μm. Formation of recording layer 40 parts of liquid A, 150 parts of liquid B, 30 parts of silicon oxide pigment (oil absorption 180 ml/100 g), 20% oxidized starch aqueous solution
Mix and stir 100 parts and 100 parts of water. The obtained coating liquid was applied in the same manner as in Example 1 to obtain heat-sensitive recording paper. Example 3 Example 2 except that 10 parts each of 2,4-dihydroxybenzophenone and 4-hydroxydimethyl phthalate were used instead of 20 parts of 2,4-dihydroxybenzophenone in the preparation of Solution B. A thermosensitive recording paper was obtained in exactly the same manner. Example 4 In preparing Solution B, 10 parts each of 2,4-dihydroxybenzophenone and 2-hydroxy-4-benzyloxybenzophenone were used instead of 20 parts of 2,4-dihydroxybenzophenone. A thermosensitive recording paper was obtained in the same manner as in Example 2 except for the following. Comparative Example 1 A thermosensitive recording paper was obtained in exactly the same manner as in Example 1 except that 4-hydroxydimethyl phthalate was not used in the preparation of liquid B. Comparative Example 2 A thermosensitive recording paper was obtained in exactly the same manner as in Example 2 except that 2,4-dihydroxybenzophenone was not used in the preparation of liquid B. The six types of thermal recording paper thus obtained were recorded using a thermal facsimile (Hitachi HIFAX-700 model), and the color density (D ₁ ) was measured using a Macbeth densitometer (RD-100R model, using an amber filter). The results are shown in Table 1. Furthermore, after leaving this recorded thermal paper at room temperature for 24 hours,
Color density (D ₂ ) was measured again using a Macbeth densitometer. Then, calculate the residual rate of color density (%) = (D ₂ / D ₁ ) × 100,
The results are listed in Table 1.

【table】

[Table] As is clear from the results in Table 1, the heat-sensitive recording material of the present invention was a recording material that had excellent recording sensitivity, improved printing decoloration phenomenon, and excellent high-speed recording suitability.

Claims (1)

[Claims] 1. A recording layer containing a colorless or light-colored basic dye, hydroquinone monobenzyl ether, and at least one compound represented by the following general formula [] or [] is provided on a support. A heat-sensitive recording material characterized by: [In the formula, R ₁ and R ₂ are each a C _1-8 alkyl group,
It represents a phenyl group [formula] or a benzyl group [formula], and R ₃ and R ₄ represent a hydrogen atom, a chlorine atom, a hydroxyl group, or a C _1-8 alkoxyl group. ] [In the formula, R ₅ , R ₆ and R ₇ each represent a hydrogen atom, a chlorine atom, a hydroxyl group, a C _1-12 alkoxyl group, a phenoxy group or a benzyloxy group. ]