JPH0141517B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal recording paper, and more particularly to a thermal paper that has improved color development sensitivity and develops clear colors at low temperatures.

It has been known for a long time that a colorless or light-colored color-forming substance such as crystal violet lactone reacts with a phenol compound to form a color, and the application of this reaction to thermal paper was described, for example, in U.S. Pat. No. 3,539,375. It is publicly known.

However, there are many drawbacks that need to be addressed in response to recent advances in recording devices, diversification of applications, high speed response, and high sensitivity. For example, in thermal printers, thermal facsimiles, etc., if the coloring sensitivity of thermal recording paper is insufficient, the power consumption increases and the printing speed decreases, so it is necessary to increase the coloring sensitivity.

As a method of improving the color development sensitivity of such thermal recording paper, an example of using waxes in combination of a color-forming substance and a phenol compound is described in JP-A-48-19231, and a method using nitrogen-containing compounds, etc. An example of using a sensitivity improver is JP-A-49-
34842, respectively.

In heat-sensitive recording paper, a color-forming substance and a phenol compound are dispersed in the form of fine particles in the heat-sensitive coating layer, or are stably separated and present in different layers, but when heated, one of the two components melts or sublimates. Alternatively, it is thought that both components melt or sublimate, come into close contact with each other, mix, and develop thermal color. Therefore, each component of the reactive coloring agent must be colorless to light-colored crystals or solids at room temperature, and the melting point must be 70°C.
Those that completely liquefy and/or vaporize at temperatures above 150-200°C are preferred.

U.S. Pat. No. 3,539,375 describes 4,4'-isopropylidene diphenol (melting point 156°C) as one example of a suitable phenolic compound for use in this purpose, and it is widely used today. However, in order to develop color by thermal melting as described above, it is difficult to develop a clear color unless the temperature is considerably high (for example, 140 to 150°C). However, as mentioned above, in order to increase the color development sensitivity of thermal recording paper in response to the increasing speed of recording devices, the melting point of each component of the reactive coloring agent must be as low as possible, and the eutectic point must be lower than any of the components. Reacts at both hot and low temperatures (e.g. 90-120℃),
In addition, it is preferable to obtain clear color development. Also,
Methyl p-hydroxybenzoate (melting point 126-128
℃), but even though the melting point is low, the molecular weight is small and the heat volatility is considered, which is not very preferable in practice.

As a result of studying various phenolic compounds, the present inventors discovered that by combining a color-forming substance and a specific phenolic compound, a material with excellent sensitivity that can produce vivid colors even at lower temperatures (for example, 90 to 120 degrees Celsius) than before has been developed. It has been discovered that thermosensitive recording paper can be obtained. The phenol compound of the present invention referred to here has the formula It is 4-butoxy-4'-hydroxy-diphenyl sulfone represented by

The color-forming substance may be any substance that can develop color by reacting with a phenol compound.
For example, crystal violet lactone, malachite green lactone, 3,3-bis(paradimethylaminophenyl)-4,5,6,7-tetrachlorophthalide, benzo-β-naphthospiropyran, 3-methyl-di- β-naphthospiropyran, 1,3,3-trimethyl-6'-chloro-8'-
Methoxyindolinobenzospiropyran, N-phenylrhodamine lactam, 3-ethylamino-
6-chlorofluorane, 3-morpholino-5,6
-benzofluorane, 3-diethylamino-6-
Methyl-7-chlorofluorane, 3-diethylamino-6,7-dimethylfluorane, 3-dimethylamino-7,8-benzofluorane, 3-diethylamino-6-methoxyfluorane, 3-diethylamino-7-dimethylfluorane benzylaminofluorane,
3-diethylamino-7-anilinofluorane,
3-diethylamino-5,6-benzo-7-benzylaminofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3-N
-Ethyl tolylamino-6-methyl-7-anilinofluorane, 3-diethylamino-7-(N
Examples include, but are not limited to, -3-trifluoromethylphenyl)aminofluorane.

Furthermore, the phenolic compound of the present invention generally has a 70%
Other phenol compounds that have the property of liquefying or vaporizing at temperatures above ℃ and reacting with the color-forming substance to form a color, such as 4,4'-isopropylidene diphenol, 4,4'-isopropylidene bis(2-
chlorphenol), 4,4'-isopropylidene bis(2-tert-butylphenol), 4,4'-sec-butylidene diphenol, 4,4'-cyclohexylidene diphenol, 4-phenylphenol, 4- Hydroxy diphenoxide, methyl p-hydroxybenzoate, phenyl p-hydroxybenzoate, 4-hydroxyacetophenone, salicylic acid anilide, novolac type phenolic resin, halogenated novolac type phenolic resin, α-naphthol, β-naphthol, 2 ,2-bis-(4-
It can also be used in combination with (hydroxyphenyl)-n-heptane.

The phenol compound and color-forming substance of the present invention are separately ground in water or in an organic solvent using a ball mill, sand grinder, etc. together with a surfactant, binder, or dispersant if necessary, and then applied to a support by a conventional method. Heat-sensitive recording paper is obtained by coating and drying.

The phenol compound of the present invention is produced, for example, by the following method.

Bisphenolsulfone 5g, ethanol 40
ml, 10 ml of sodium ethoxide, and 2.7 g of butyl bromide were heated under reflux for 5 hours. The reaction solution is then concentrated under reduced pressure, the residue is diluted with water, and unreacted butyl bromide and by-product 4,4'-dibutoxy-diphenyl sulfone are removed with an organic solvent. The aqueous layer is made acidic and extracted with chloroform (unreacted bisphenolsulfone is removed because it is insoluble in chloroform). When the resulting crude product is purified by silica gel column chromatography, it has a melting point of 118-119
4-butoxy-4'-hydroxy-diphenylsulfone is obtained.

Next, the present invention will be explained in more detail with reference to Examples.

Comparative Example Part A Crystal violet lactone 1 part 5% polyvinyl alcohol 5 parts Water 40 parts Part B 4,4'-isopropylidene diphenol 5 parts 5% polyvinyl alcohol 25 parts Water 20 parts Example 1 Part A Comparative example Solution A and Solution B 4-butoxy-4'-hydroxy-diphenylsulfone 5 parts 5% polyvinyl alcohol 25 parts Water 20 parts The liquids are mixed to obtain a coating liquid for thermal recording paper. The coating solution is applied to the surface of high-quality paper having a basis weight of 50 g/m ² so that the dry coating amount is 4 g/m ² . The obtained thermal paper was dried at 50°C in a dryer, and the paper was colored on a hot plate heated to 80 to 150°C at a pressure of 1.5 kg/cm ² and a pressure contact time of 5 seconds.
The concentration was measured using a photoelectric densitometer. The results are shown in FIG.

Further, when the thermal recording papers obtained in Examples 1 and 2 were recorded by facsimile, the dynamic color density was high and clear images were obtained.

[Brief explanation of drawings]

Figure 1 shows the relationship between temperature and color density measured with a photodensitometer, and shows a comparative example and Example 1.
This is thermal paper treated with the following formula.

Claims (1)

[Claims] 1. A thermosensitive recording paper with improved color development sensitivity, which is characterized by containing a color-forming substance that is usually colorless or light-colored and 4-butoxy-4'-hydroxy-diphenyl sulfone.