JPH0542360B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a thermal recording paper, and particularly to a thermal recording paper which has excellent color development and other recording suitability, and whose colored image is stable against fingerprints and the like. (Prior technology) Thermal recording paper that utilizes the heat-generating color reaction between fluoran colorless dyes, phenols, and organic acids was developed by Tokko Sho.
It has been published in publications such as Publication No. 45-14039 and has been widely put into practical use. These thermosensitive recording papers are used in a wide range of fields, including measurement recorders, computers and information communication terminals, facsimile machines, and automatic ticket vending machines. These recording devices are equipped with a heating element such as a thermal head or a thermal pen, and when this element is heated, color is generated and a recording is obtained. Recently, as applications have diversified and equipment has become more sophisticated,
The quality requirements for thermal recording paper are also becoming more sophisticated. For example, A4 in facsimile
What used to take several minutes to record in paper format is now recorded in less than one minute. Under these circumstances, methods for improving the sensitivity of thermal recording paper include, for example, waxes (Japanese Unexamined Patent Publication No. 48-19231), nitrogen-containing compounds (Japanese Unexamined Patent Publication No. 49-34842), and phthalate esters (Unexamined Japanese Patent Publication No. 49-34842). It has been proposed to use additives such as 116690 (1984), but the color development sensitivity, stability of the color image,
A paper that satisfies the performance requirements of thermal recording paper in a well-balanced manner, such as recording suitability and background fog, has not yet been obtained. In heat-sensitive recording paper, a color-forming substance and a phenol compound are present in the heat-sensitive recording layer as finely dispersed particles, and when heated, one of the two components dissolves or the two components eutectically fuse with each other. It is thought that color develops upon close contact. U.S. Pat. No. 1,509,375 describes 2,2-bis(4'-hydroxyphenyl)propane (BPA, melting point 156°C) as one example of a suitable phenolic compound for use in this purpose. It is a compound that is widely used today, but
In order to develop color by thermal melting as described above, it is difficult to develop clear color unless the temperature is considerably high (140 to 150°C). For this reason, the compounds mentioned above are used as sensitivity improvers in thermal recording paper, but these compounds have difficulty dissolving color-forming compounds and phenolic compounds, are sublimable, or are hot-melting. It requires a lot of energy and is slow, making it impractical. (Objective of the Invention) An object of the present invention is to provide a heat-sensitive recording material with excellent color development sensitivity that is practical and can be used in a wide range of applications without having the above-mentioned drawbacks. (Structure of the Invention) The heat-sensitive recording material of the present invention comprises at least one colorless or light-colored color-forming substance and a phenolic compound, 2,2-bis(4'-hydroxyphenyl).
propane, 1,1-bis-(4-hydroxyphenyl)-cyclohexane and 4,4'-thiobis-(3-methyl6-tert-butylphenyl),
This is a heat-sensitive recording material characterized by containing a benzyl biphenyl compound represented by the following formula (1) as a sensitizer in a heat-sensitive recording layer. Formula (1) As the color-forming substance of the present invention, what is generally known as a colorless to light-colored fluoran dye can be used. Although not particularly limited,
Examples include the following: 3-diethylamino-6-methyl-7-anilinofluorane (black) 3-(N-ethyl-P-toluideino)-6-methyl-7-anilinofluorane (black) 3-diethylamino-6-methyl- 7-(ortho, para-dimethylanilno)fluorane (black) 3-(N-isoamyl-N-ethyl)-6-methyl-7-anilinofluorane (black) 3-pyrrolidino-6-methyl-7- Anilinofluorane (black) 3-piperidino-6-methyl-7-anilinofluorane (black) 3-(N-cyclohexyl-N-methylamino)
-6-Methyl-7-anilinofluoran (black) 3-diethylamino-7-(ortho-chloroanilino)fluoran (black) 3-diethylamino-7-(meta-trifluoromethylanilino)fluoran (black) 3- Diethylamino-6-methyl-chlorofluoran (red) 3-diethylamino-6-methyl-fluoran (red) 3-cyclohexylamino-6-chlorofluoran (orange) On the other hand, the phenolic compounds of the present invention include, as described above, 2,2-bis(4'-hydroxyphenyl)propane (bisphenol A), 1,1-bis-(4-hydroxyphenyl)-cyclohexane and 4,4'-thiobis-(3-methyl 6-tert −
butylphenyl) is used as a color developer. When only bisphenol A is used as a color developer,
It has the disadvantage that white powder forms on the image area when touched with fingers, etc., which covers the image and makes it unclear.It also has the disadvantage of being inferior to heat-sensitive recording materials in terms of color development sensitivity, heat-resistant storage stability, humidity-resistant storage stability, whiteness, etc. It has not been possible to satisfy the required performance in a well-balanced manner. The present inventors have conducted intensive studies on these problems and have arrived at the present invention. That is, (1) 1,1- for 1 part by weight of bisphenol A
0.2 to 0.25 parts by weight of bis-(4-hydroxyphenyl)-cyclohexane, 4,4'-thiobis-(3
-Methyl 6-tert-butylphenyl) in a mixture of 0.2 to 1 part by weight causes less dusting and improves color development sensitivity compared to using bisphenol A alone due to lowering of melting point due to eutectic. (2) When used together with the benzyl biphenyl compound of the present invention, a heat-sensitive recording material using only bisphenol A as a color developer can be produced with excellent color development sensitivity; however, it is necessary to use a color developer system with the above combination. It was found that the color development sensitivity was further improved and that it was preferable in terms of image storage stability and whiteness. For 1 part by weight of these phenolic compounds,
Preferably, 0.1 to 2 parts by weight of benzylbiphenyl is used. The benzyl biphenyl used in the present invention may be any compound in the ortho, meta, or para form, or may be used as a mixture. The thermal recording paper of the present invention can be obtained by the following method. That is, a color-forming compound, a phenolic compound, and benzylbiphenyl are separately ground and dispersed in a medium containing a binder at an appropriate concentration using a grinder such as a ball mill to a particle size of several microns or less, and the resulting product is The resulting dispersion is mixed to form a single solution, to which fillers, brighteners, wetting agents, preservability improvers, lubricants, antifoaming agents, etc. are added as necessary. Coat on a support and dry. As binders, media, fillers, brighteners, wetting agents, lubricants, antifoaming agents, and supports, various materials used for producing conventional thermal recording paper can also be used in the present invention. I can do it. Conventional coating methods and drying methods can also be used as they are. (Examples) In order to make it easier to understand the present invention, examples are shown below, but the following examples do not limit the present invention. Parts in the examples indicate parts by weight. Example 1 Liquid A (dye dispersion) 3-(N-cyclohexyl-N-methyl-amino)
-6-Methyl-7-anilinofluorane 2 parts 10% polyvinyl alcohol 4 parts Water 4 parts Part B 2,2-bis(4'-hydroxyphenyl)-propane 3 parts 1,1-bis-(4- Hydroxyphenyl)-cyclohexane 2 parts 4,4'-thiobis-(3-methyl 6-tert-butylphenol) 1 part ethylene bisstearamide 1 part 10% polyvinyl alcohol 18 parts C Liquid P-benzylbiphenyl 2 parts 10% polyvinyl alcohol 4 parts Water 4 parts Three liquids A, B, and C are each ground and dispersed in a separate ball mill to a particle size of 1 to 5 μm. Next, the dispersion liquid is mixed in the proportions shown below to prepare a coating liquid. 10 parts of solution A 20 parts of solution B 10 parts of solution C 17 parts of calcium carbonate (50% dispersion) Apply 5.5 parts of this coating solution to one side of a 50g/ ^m2 base paper.
The sheet was coated and dried to give a smoothness of 300 to 500 seconds using a ^{supercalender} to produce heat-sensitive recording paper. The test results are shown in Table 1 (described later). Examples 2 and 3 In Example 2, m-benzylbiphenyl was used in place of P-benzylbiphenyl in Solution C of Example (1), and in Example 3, the same amount of 0-benzylbiphenyl was used. Thermosensitive recording paper was prepared in the same manner as in (1). Comparative Example 1 A thermal recording material was prepared using a coating solution in which 30 parts of Solution B of Example (1) was added without adding Solution C. Comparative Example 2 5 parts of benzyl p-hydroxybenzoate, 1 part of 4,4'-thiobis-(3-methyl 6-tert-butylphenyl) and 1 part of ethylene bisstearamide were used in place of Solution B in Example (1). Example using
A thermosensitive recording material was obtained in the same manner as in (1). Comparative Example 3 2,2-bis(4'-
A heat-sensitive recording material was obtained in the same manner as in Example (1) using 6 parts of (hydroxyphenyl)-propane and 1 part of ethylene bisstearamide. Comparative Example 4 3 parts of 2,2-bis(4'-hydroxyphenyl)propane and 3 parts of 1,1-bis-(4-hydroxyphenyl)-cyclohexane were used in place of Solution B in Example (1).
A heat-sensitive recording material was obtained in the same manner as in Example (1) using 1 part of ethylene bisstearamide and 1 part of ethylene bisstearamide. Comparative Example 5 2,2-bis(4'-
hydroxyphenyl)-propane 5 parts, 4,4'-
A heat-sensitive recording material was obtained in the same manner as in Example (1) using 1 part of thiobis-(3-methyl 6-tert-butylphenol) and 1 part of ethylene bisstearamide. The following comparative tests were conducted on the heat-sensitive recording materials produced in Examples 1 to 3 and the comparative heat-sensitive recording materials produced in Comparative Examples 1 to 5. (a) Recording was performed using Toshiba FAX COPIX-6300, and color density and background fog were measured. Macbeth Densitometer RD-104 was used for measurement. (b) Moisture resistance was determined by leaving the surrounding image under conditions of 40° C. and 90% RH for one day, and then measuring the background fog in the blank area and the image density remaining rate in the recorded area. (c) Oil resistance is determined by applying castor oil to the recording area at a concentration of 0.5 g/m ² and measuring the remaining image density of the recording area after leaving it for one day at 25°C and 65% RH. It was measured. The results of these tests are shown in Table 1.

【table】

[Table] (Effects of the invention) The effects of the present invention include the following points. (1) Due to its excellent thermal response, clear recording with high density can be obtained even in high-speed, high-density recording. (2) The skin is white and does not discolor over time. (3) There is little discoloration of colored images due to fingerprints, humidity, oil, and heat, and there is little background smearing in blank areas, so the so-called storage stability is greatly improved.

Claims (1)

[Claims] 1. A colorless or light-colored color-forming substance, 2,2-bis(4'-hydroxyphenyl)propane, 1,1-bis-(4-hydroxyphenyl)-cyclohexane, which causes the color-forming substance to develop color by heating, and 4,
1. A heat-sensitive recording paper comprising 4'-thiobis-(3-methyl-6-tert-butylphenol) and benzylbiphenyl as a sensitizer in a heat-sensitive coloring layer.