JPH0160437B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a heat-sensitive recording sheet,
More specifically, the present invention relates to a highly sensitive color-forming heat-sensitive recording sheet. In recent years, thermal recording methods have many features such as non-impact, no noise during recording, no need for developing and fixing, and easy maintenance and management of equipment, so they are used in a wide variety of applications, including various printers and telephone facsimile machines. has been done. Particularly in telephone facsimile, demand for heat-sensitive systems is increasing significantly, and speeds are being increased to reduce transmission costs. In response to such increased speed of facsimile, there has been a demand for higher sensitivity of heat-sensitive recording materials. High-speed facsimile can print standard A4 documents.
Since data is sent and received in 20 seconds to 1 minute, the current flowing through the facsimile's thermal head is extremely short, 1 to 2 milliseconds, and the generated thermal energy is transferred to the thermosensitive recording sheet to form an image. It is something. In order to carry out an image forming reaction using thermal energy transmitted in such a short period of time, it is necessary to use a thermosensitive recording sheet with excellent thermal responsiveness. Furthermore, if the conditions in which the device is used are at temperatures as low as 10° C. or lower, this requirement will inevitably become even more stringent. Normally, a dye precursor and a color developer are required components for a heat-sensitive recording sheet, but Japanese Patent Publication No. 43-4160 discloses that a method for increasing sensitivity is to incorporate a heat-fusible substance into the heat-sensitive layer. has been done. A thermofusible substance has the function of promoting a color reaction by dissolving or incorporating either a dye precursor or a color developer, or both, when it is melted by the transferred thermal energy. . However, the thermofusible substance itself does not directly develop color, but has a sensitizing effect as well as a so-called dilution effect, which causes a decrease in concentration due to blurring or coating the printed area, and furthermore, it has a so-called dilution effect, which causes a decrease in density due to smearing or coating the printed area. Since it also has the disadvantage of states king, there is a limit to the sensitizing effect when used alone. Therefore, a better method would be to improve the thermal responsiveness of dye precursors or color developers that are involved in direct color development.However, dye precursors are currently limited in their selection due to their properties after color development, cost, manufacturing issues, etc. It is actually difficult to find dye precursors with excellent thermal responsiveness among these narrow ranges. In other words, we thought that selecting a color developer with good thermal responsiveness would be a good way to increase the sensitivity of a heat-sensitive sheet, and as a result of a wide range of color developer studies, we published the product described in JP-A-54-74762. p with
-It was found that benzyl oxybenzoic acid ester has excellent thermal responsiveness. However, due to the lack of stability of colored images, as a result of investigation, it was discovered that by using p-benzyloxybenzoic acid benzyl ester together, it was found that the stability of the image was improved and it also had a sensitizing effect. Showa 56
- As shown in No. 195220. However, due to changes in recording devices due to faster recording speeds and the need for high density recording under harsh conditions of 10°C or less, the present inventors developed a thermosensitive film using p-hydroxybenzoic acid ester. In the recording sheet, the low-temperature coloring sensitivity was improved by using p-benzyloxybenzoic acid benzyl ester and waxes with a melting point of 60°C to 110°C.
He made the invention described in No. 57-69084. However, in order to enable mutual communication with conventional low-speed and medium-speed machines, even in high-speed machines, the amount of heat transferred to the heat-sensitive recording sheet may change depending on the electric transmission mode. Specifically, in the case of low-speed or medium-speed transmission mode,
Since the time for heat transfer becomes longer, in order to keep the amount of heat transfer energy constant, the temperature of the heat head, which is a heating element, is kept at a relatively low temperature, or the scanning line density is reduced. Therefore, the situation becomes extremely difficult for high-density recording in a low-temperature atmosphere. Therefore, it became necessary to further increase the sensitivity, and as a result of intensive studies, we developed a system that uses both benzyl p-benzyloxybenzoate and waxes with a melting point of 60°C or higher, and also added a terephthalic acid ester compound with a melting point of 60°C or higher. It has been found that the inclusion of the compound has an extremely excellent synergistic effect in improving coloring efficiency. The melting point of both waxes and terephthalic acid ester compounds used in the present invention is limited to 60°C or higher in order to prevent fogging of the skin during the drying process during coating of the heat-sensitive layer. Terephthalic acid ester compounds (e.g. terephthalic acid diethyl ester: mp43.2℃)
) or waxes with a melting point of less than 60℃ (e.g. lanolin: MP36℃~40℃), or both in combination can improve coloring efficiency, but it causes fogging on the background, making it impractical. .
Furthermore, in Japanese Patent Application No. 57-69084, the upper limit of the melting point of waxes was set at 110°C, but in the present invention, waxes with a melting point exceeding 110°C (for example, ethylene bisstearamide: m.
Even when used in combination with a diluent (p. 141 to 146°C, etc.), the sensitivity improvement effect was large, and there was almost no dilution effect, and a practically satisfactory result was obtained. Therefore, in more detail, the "terephthalic acid ester compound with a melting point of 60°C or higher" used in the present invention
For example, terephthalic acid monoethyl ester (mp165℃), terephthalic acid monopropyl ester (mp127-129℃), terephthalic acid monoisopropyl ester (mp166℃), terephthalic acid monobutyl ester (mp122-124℃), terephthalate. Acid monoisobutyl ester (mp151-154℃),
Terephthalic acid mono-n-octyl ester (mp82
~84℃), terephthalic acid monocyclohexyl ester (mp160~162℃), terephthalic acid dimethyl ester (mp140℃), terephthalic acid di-t-butyl ester (mp118℃), terephthalic acid dicyclohexyl ester (mp75~80℃), 2 -Methyl terephthalic acid dimethyl ester (mp73℃), 2
-Chloro-terephthalic acid dimethyl ester (m.
p.60℃), 2,5-dichloro-terephthalic acid dimethyl ester (mp136℃), 2-bromo-5-chloro-terephthalic acid diethyl ester (mp115
~116.5℃), terephthalic acid diphenyl ester (mp191℃), etc. Next, "waxes" with a melting point of 60°C or higher used in the present invention include animal-based waxes such as beeswax and Chinese wax, plant-based waxes such as Candelilla wax and carnauba wax, Montan wax, etc. Mineral waxes, petroleum waxes such as paraffin waxes and microcrystalline waxes, modified waxes such as montan wax derivatives, paraffin wax derivatives, and microcrystalline wax derivatives, hydrogenated waxes such as Castor wax, and low molecular weight waxes. Synthetic waxes for polyethylene and its derivatives, other saturated fatty acid amides such as lauric acid amide, stearic acid amide, palmitic acid amide, palmic acid amide, behenic acid amide, etc., unsaturated acids such as oleic acid amide, erucic acid amide, ricinoleic acid amide, etc. fatty acid amide, and N-
Cyclohexyl stearic acid amide, N-cyclohexyl palmitic acid amide, N-ethyl stearic acid amide, N-ethyl palmitic acid amide,
Examples include amide waxes of fatty acid amide derivatives such as N-stearyl stearamide, N-stearylbenzamide, phenylacetic acid N-stearylamide, N-hydroxymethyl stearamide, and ethylene bisstearamide, which may be used alone or in combination with A combination of two or more types can be used as a fine powder or emulsion. Furthermore, in terms of quantity, each of the following three compounds was added to the color developer p-oxybenzoic acid benzyl ester, "p-benzyloxybenzoic acid benzyl ester", "waxes", and "terephthalic acid ester compound".
The object of the present invention can be achieved by using 10 to 60% by weight of the three in combination, preferably in an amount that does not exceed 1.2 times the total weight of the three components based on benzyl p-hydroxybenzoic acid ester. Note that excessive addition is undesirable from a cost standpoint, wastes transferred thermal energy, and does not directly develop color by itself, resulting in a dilution effect that lowers the density of printed areas.Furthermore,
The negative effects of Kas and States King are also great. The present invention provides p-hydroxybenzoic acid benzyl ester, p-benzyloxybenzoic acid benzyl ester, waxes with a melting point of 60°C or higher, and a melting point of 60°C or higher.
The terephthalic acid ester compounds at a temperature of ℃ or higher are crushed and dispersed into fine particles using a crusher, either separately or simultaneously.
Similarly, a coating liquid is prepared by mixing with the pulverized and dispersed dye precursor, binder, pigment, etc., and adding various additives such as a surfactant or brightener as necessary. Next, the dye precursor, binder, and pigment used in the present invention will be explained below, but the present invention is not limited thereto unless the gist of the present invention is exceeded. (1) Dye precursor Dye precursors commonly used for thermal paper can be used, such as crystal violet lactone, 3-diethylamino-7-methylfluoran, 3-diethylamino-6-chloro-7-methylfluoran, 3-diethylamino-6-methyl-7-chlorofluoran, 3-diethylamino-7-anilinofluorane, 3-diethylamino-7-(2-chloroanilino)fluoran, 3-dibutylamino-7-(2-chloroanilino) Fluoran, 3-diethylamino-7
-(3-chloroanilino)fluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-(N-ethyl-p-toluidino)-
6-methyl-7-anilinofluorane, 3-
(N-methylcyclohexylamino)-6-methyl-7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, and the like. (2) Binders For example, starches, hydroxyethyl cellulose, methyl cellulose, polyvinyl alcohol, styrene-maleic anhydride copolymer, styrene-butadiene copolymer, polyacrylamide, etc. (3) Pigments For example, diatomaceous earth, talc, kaolin, calcined kaolin, calcium carbonate, magnesium carbonate, titanium oxide, zinc oxide, silicon oxide, aluminum hydroxide, urea-formalin resin, etc. Next, the present invention will be explained in more detail with reference to Examples and Comparative Examples. The support may be paper, synthetic paper, synthetic resin film, etc., but paper is generally used. Example 1 (1) Solution A (Acid separation solution of p-hydroxybenzoic acid benzyl ester) p-hydroxybenzoic acid benzyl ester
175g Maron MS-25 (styrene-maleic anhydride copolymer sodium salt manufactured by Daido Kogyo Co., Ltd.)
25% aqueous solution) 35g Water 290g The above dispersion was pulverized and dispersed in a ball mill for 48 hours. (2) Solution B (dispersion of p-benzyloxybenzoic acid benzyl ester) p-benzyloxybenzoic acid benzyl ester 175g 10% aqueous solution of ammonium salt of styrene-maleic anhydride copolymer 87.5g Water 237.5g Above dispersion Grind and disperse in a ball mill for 48 hours. (3) Solution C (dispersion liquid of terephthalic acid ester compound) Terephthalic acid dimethyl ester (melting point 140~
142°C) 175g 10% aqueous solution of ammonium salt of styrene-maleic anhydride copolymer 87.5g Water 237.5g The above dispersion was pulverized and dispersed in a ball mill for 48 hours. (4) Liquid D (wax dispersion) Stearamide (manufactured by Kao Soap Co., Ltd., trade name: Fatty Acid Amide S, melting point 103-105°C)
150 g 10% aqueous solution of ammonium salt of styrene-maleic anhydride copolymer 75 g Water 275 g The above dispersion was pulverized and dispersed in a ball mill for 48 hours. (5) Solution E (dispersion of dye precursor) 3-diethylamino-6-methyl-7-anilinofluorane 200g Maron MS-25 24g water 276g The above dispersion was pulverized and dispersed in a ball mill for 48 hours. A liquid, B liquid, C liquid, D dispersed in this way
A heat-sensitive coating liquid was prepared using Liquid and Liquid E as shown below. Calcium carbonate (manufactured by Shiroishi Kogyo Co., Ltd., product name: Charcoal PC) ... 5g Solution A ... 17g Solution B ... 5.7g Solution C ... 5.7g Solution D ... 3.3g Solution E ... 6g 15 Weight % polyvinyl alcohol aqueous solution
...24.5g Water ...24.8g The coating liquid prepared as above was applied to base paper with a basis weight of 50g/ ^m2 so that the coating weight after drying was 7.4g/ ^m2 ,
The paper was dried at 60°C for 1 minute to produce thermal paper. Example 2 A coating liquid was prepared in the same manner as in Example 1, except that dimethyl terephthalate was replaced with monobutyl terephthalate [melting point 122-124°C] in liquid C of Example 1, and the basis weight was 50 g. / ^m2 of base paper so that the coating amount after drying is 7.4g/ ^m2 ,
It was dried at ℃ for 1 minute to produce thermal paper. Example 3 In Solution D of Example 1, ethylene bisstearamide [manufactured by Kao Soap Co., Ltd., trade name: Kao Wax EB-] was used instead of stearamide.
Example 1 except that F, melting point 141-146.5°C]
A coating solution was prepared in the same manner as above, and applied to base paper with a basis weight of 50 g/m ² so that the coating weight after drying was 7.4 g/m ² , and heated at 60°C.
The paper was dried for 1 minute to produce thermal paper. Comparative Examples 1 to 3 A heat-sensitive coating liquid was prepared as shown in the table below using liquids A, B, C, D, and E shown in the examples.
The coating amounts shown in the table below were applied to 50 g/m ² base paper after drying, and dried at 60° C. for 1 minute to prepare thermal paper.

【table】

[Table] Example 4 The thermal papers of Examples 1 to 3 and Comparative Examples 1 to 3 were heated in a super calender so that the Beck smoothness was approximately 500 seconds, and then heated using a facsimile FACOM manufactured by Fudotsu Co., Ltd.
Recordings were made using Fax621C in a thermostatic chamber set to the atmosphere shown below, and the color density was measured. a 18°C (general room temperature) b 5°C (experimental low temperature) c 0°C (experimental low temperature) The concentration was measured using a Sakura densitometer.
Measured using a PDA45 amber filter. Show results below.

[Table] As can be seen from the above table, in thermal paper using p-hydroxybenzoic acid benzyl ester, p-
Benzyloxybenzoic acid benzyl ester, melting point
By using a combination of waxes with a melting point of 60°C or higher and a terephthalic acid ester compound with a melting point of 60°C or higher, the invention including the invention described in Japanese Patent Application No. 57-69084 can be obtained.
It was found that the composition had even higher sensitivity and color development than those obtained by excluding one of them, and in particular, it was found to have a remarkable effect on high sensitivity color development in a low-temperature atmosphere.

Claims (1)

[Scope of Claims] 1. A heat-sensitive recording sheet using p-hydroxybenzoic acid benzyl ester as a color developer that reacts with a colorless or light-colored dye precursor and causes the dye precursor to develop color when heated, 1. A highly sensitive color-developing heat-sensitive recording sheet characterized by the combination of benzyl oxybenzoate, a wax having a melting point of 60°C or higher, and a terephthalic acid ester compound having a melting point of 60°C or higher. 2 For p-hydroxybenzoic acid benzyl ester, p-benzyloxybenzoic acid benzyl ester, waxes with a melting point of 60°C or higher, and melting point 60
The three terephthalic acid ester compounds above ℃
10 to 60% by weight of each, and the total weight% of the three
The highly sensitive color-forming heat-sensitive recording sheet according to claim 1, wherein the amount of p-hydroxybenzoic acid benzyl ester is not more than 1.2 times that of p-hydroxybenzoic acid benzyl ester. 3. A highly sensitive color-forming thermosensitive recording sheet according to claim 1 or 2, which uses fatty acid amide and its derivatives as the wax having a melting point of 60° C. or higher.