JPS58222888A - Heat-sensitive recording material - Google Patents

Abstract

PURPOSE:To provide the titled material excellent in color producing property at the time of high-speed recording and stability of an image, wherein a specified phenolic substance is incorporated as a color developer for developing the color of a leuco dye when being heated. CONSTITUTION:The heat-sensitive recording material comprises, on a base, a leuco dye and a phenolic substance of formula I (wherein each of R and R' is halogen, lower alkyl; each of n and m is 0, 1-4) as a color developer for developing the color of the leuco dye when being heated. Since the sheet does not required any sensitizer or any melting point lowering agent, it is excellent in response to heat, adaptability to recording and in stability and contrast of image when being preserved at high temperature and/or high humidity. In addition, the recording material is excellent also in stability in preservation at room temperature and is free from phenol odor.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat-sensitive recording material, and particularly to a heat-sensitive recording material that has excellent color development and image stability during high-speed recording.

General heat-sensitive recording materials are coated on a support such as paper or film, and contain a colorless or light-colored dye such as a leuco dye as a color former, and a phenolic compound (particularly bisphenol A) as a color developer to make the color develop when heated. A coloring system consisting of an acidic substance such as an organic acid is further provided with a heat-sensitive coloring layer in which a binder, a filler, a sensitivity improver, a lubricant, and other auxiliary agents are dispersed. -14039
No. 48-27736, etc., and has been widely put into practical use. This type of heat-sensitive/recording material obtains a colored image through an instantaneous chemical reaction between a coloring agent and a color developer during heating (a thermal printer or facsimile machine with a built-in thermal head is used for heating). Therefore, compared to other recording materials, records can be obtained in a short time using relatively simple equipment without complicated processing such as development and fixing.
Due to its advantages of low noise generation, low environmental pollution, and low cost, it is used for copying books, documents, etc., as well as for recording various information and measuring instruments such as electronic computers, facsimiles, telex machines, medical measuring instruments, etc. Useful as a material. On the other hand, in recent years, along with the development of society, there has been an increasing demand for higher speed and higher density recording. For this reason, there is a strong desire not only to increase the speed of the recording apparatus itself, but also to develop recording materials that can support this speed. Therefore, from this point of view, Japanese Patent Application Laid-Open Nos. 53-39139, 53-26139, 53-5636, and 53-11036 contain various waxes, fatty acid amides, It has been proposed to add a heat-melting substance with a low melting point, such as alkylated biphenyls, substituted biphenylalkanes, coumarins, and diphenylamines, as a sensitizer (or melting point depressant). However, in the method of adding a sensitizer, it is necessary to melt the sensitizer without rinsing it prior to the color development reaction, so it is not possible to obtain sufficient thermal responsiveness in high-speed recording where only a small amount of heat is supplied in a short pulse. In addition, since the sensitizer in the coloring layer melts, there are problems in recording suitability, such as adhesion of residue to the thermal head, smearing, trailing, ghosting, and other problems. Furthermore, when stored at high temperatures and/or high humidity, fogging occurs over time and often reduces the contrast of recorded images. Therefore, it is desirable for a heat-sensitive recording material for high-speed recording to have a structure in which no sensitizer is added. However, the temperature of colorless or light-colored color-forming dyes used in heat-sensitive recording materials is usually 160 to 240℃.
Therefore, in order to construct a heat-sensitive color forming layer suitable for high-speed recording without adding an i-sensitizer, it is essential to use a color developer that has a low melting point and has a high ability to develop color from the color former. By the way, regarding acidic substances, especially phenolic compounds, to be combined with colorless or light-colored dyes, Japanese Patent Publication No. 1973-
Although it is described in many documents including No. 14039, bisphenol A is widely used because of its stable quality, low price, and easy availability. However, since bisphenol A has a high melting point of 156-158℃, its thermal sensitivity is low and its thermal coloring temperature is high.
1.・□There is a drawback. In contrast, phenolic compounds with low melting points, such as 4-t-butylphenol (melting point 9
4-99°C), α-naphthol, (melting point 95-96°C)
When monophenols such as β-naphthol (melting point 119-122°C) are used, the storage stability of the heat-sensitive recording material is poor, and not only does it gradually become cloudy even at room temperature, but it also has a strong so-called phenol odor, making it difficult to put into practical use. Not the point. Sunta Special Publication No. 12819/1986 describes 2゜2-bis(4'-hydroxyphenyl) normal hexane (melting point 99-10
3℃) in JP-A No. 55-27253 with ij: 1, 1
-It is stated that a heat-sensitive recording material with high heat sensitivity, storage stability, and good color development can be made by using bis(4'-hydroxyphenyl) alkanes (the number of carbon atoms in the alkane is 3 to 13). However, all of these substances are difficult to synthesize and have problems in availability. Furthermore, JP-A-56-144
No. 193 describes that the lower alkyl ester of p-hydroquine benzoic acid or benzyl nitrite is easy to synthesize, and that a highly sensitive heat-sensitive recording material can be made using the cleaved material. The phenolic compound tends to discolor over time, and it also has storage disadvantages such as precipitation of crystals of the phenolic compound (so-called white powder phenomenon).

As described above, conventional heat-sensitive recording materials for high-speed recording, those using sensitizers or melting point depressants, and those without, each have advantages and disadvantages, and none of them can be considered practical.

The first object of the present invention is to provide a heat-sensitive recording material that does not use a sensitizer or a melting point depressant and therefore has excellent thermal response, recording suitability, storage stability even under high temperature and/or high humidity, and image contrast. It is.

The second object of the present invention is to provide an extremely practical thermal recording material that has excellent storage stability at room temperature, no phenol odor, and no problems in availability despite the use of a low-melting phenolic compound. The goal is to provide the following.

That is, the heat-sensitive recording material of the present invention is a heat-sensitive recording material containing at least one leuco dye and a phenolic substance represented by the following general formula (+) as a color developer for developing the leuco dye. This is a heat-sensitive recording material characterized by having a coloring layer.

When a plurality of substituents R, R' are bonded to the talene nucleus, these substituents R, R,' may be the same or different. As the lower alkyl group, an alkyl group having 1 to 4 carbon atoms is usually preferred, and as the nitrogen atom, chlorine, bromine, etc. are preferred.

In the present invention, the leuco dye and the color developer made of a phenolic substance represented by the general formula (1) may be on the same support or may be on separate supports. If they are on separate supports, they are stacked on top of each other to develop color, and after color development, they are separated.

The phenolic substance represented by the general formula (1) used in the present invention can be easily produced in high yield and with high purity by reacting monothionohydroquinone with the corresponding halogenomethylnaphthalene derivative under argalic conditions. , and can be synthesized relatively inexpensively.

Leuco dyes used in combination with such phenolic substances include conventionally known colorless or light-colored color-forming dyes such as triphenylmethane, fluofy, phenothiazine, auramine, and spiropyran. Examples include the following:

Crystal violet lactone 3-diethylamino-6-methyl-7-anilinofluorane 3-(N-ethyl-p-toluidino)-6-methyl-7
-anilinofluorane 3-diethylamino-6-methyl-7-(o.

p-dimethylanilino)fluoran 3--ffo li-)/-6-liver ″ −″ −
7-ri ″1.

Luolan 3-piperidino-6-methyl-7-anilinofluoran 3-(N-cyclohexyl-N-methylamine)-6-
Methyl-7-anilinofluorane 3-diethylamine-
7-(o-chloroanilino)fluoran 3-diethylamino-7-(m-)lifluoromethylanilino)fluoran 3-diethylamino-6-methyl-7-chlorofluoran 3-diethylamino-6-methylfluoran 3-cyclo Hexylamino-6-chlorofluorane The ratio of the color-forming dye and the phenolic substance of formula (1) in the heat-sensitive coloring layer is preferably about 1:1 to 6 (by weight).

Specific examples of the phenolic substance represented by the general formula (+) include those shown below.

In addition, in order to bind and support the heat-sensitive coloring layer of the present invention on the support, various conventional binders may be appropriately used, such as polyvinyl alcohol, methoxy cellulose, hydroxyethyl cellulose, carboxomethyl cellulose, Water-soluble materials such as polyvinylpyrrolidone, polyacrylamide, polyacrylic acid, starch, and gelatin, or water-based emulsion type materials such as polystyrene, vinyl chloride-vinyl acetate copolymer, and polybutyl methacrylate can be used as binders. .

If necessary, conventional auxiliary additives such as calcium carbonate, silica, alumina,
Fine powders such as magnesia, talc, titania, barium sulfate, and aluminum stearate can be added to improve the clarity of colored images.

The heat-sensitive recording material of the present invention is produced by applying a coating liquid for forming a heat-sensitive layer containing the above-mentioned components onto a suitable support such as paper, synthetic paper, or a planetary film and drying it. It is used in the recording field, especially as a heat-sensitive recording material for high-speed recording.

According to the present invention, a heat-sensitive recording material exhibiting the following excellent properties can be obtained by using the phenolic substance represented by the general formula (1).

(1) Highly sensitive heat-sensitive recording materials can be produced without the need for sensitizers or melting point depressants. In particular, because it has excellent thermal response, high-density, clear images can be obtained even in high-speed, high-density recording.

(2) Excellent recording suitability without problems such as adhesion of debris or sticking to the thermal head.

(3) The colored image is extremely stable without fading over time or causing white powder phenomenon.

(4) The phenolic compound of the above formula can be easily synthesized, so there are no problems in obtaining it, and it can be obtained in high yield, with high purity, and at a relatively low cost.

(5) Those using thin base paper or film as a support are particularly excellent as thermal recording materials for infrared and strobe type thermal copying machines6..1.

(6) It is possible to reduce the amount of coating and improve production efficiency.

Next, examples of the present invention will be shown. Note that both "parts" and "%" are based on weight. However, the present invention is not limited to this example.

Example A mixture of the following formulations was pulverized and dispersed in a magnetic ball mill for 2 days to prepare liquids A, B and C.

a [Prescription 10% aqueous solution of hydroquinoethyl cellulose 20 parts water

6o part B liquid formulation 4-(1-methylnaphthyl)mercaptopheno 2
10% aqueous solution of 09-hydroxyethylcellulose 20 parts water

6o part C liquid prescription calcium carbonate 2
5% aqueous solution of 0 parts methylcellulose
20 parts water
(A) obtained as in 60 parts or more
~ (0) Using the liquid, prepare a thermosensitive coloring layer liquid with the following composition,
Dry coating amount 4-5 on commercially available high-quality paper with standard basis weight 501/m2
The heat-sensitive recording material of the present invention (a )made.

Thermosensitive coloring layer liquid [A] liquid 10 parts [B] liquid 30〃(0') liquid
3011 Comparative Example 1 A heat-sensitive recording material (b) was prepared in the same manner as in the example except that the following CD) i was used instead of the liquid [B] in the example.

[D] Liquid bisphenol A
20 parts” 10% human 1-xyethylcellulose dissolved in water*
ion water
60 Comparative Example 2 A heat-sensitive recording material (C) was prepared in the same manner as in Example except that the following liquid E''J was used instead of liquid CB) in Example.

[E″lti.

p-hydroxybenzoic acid benzyl ester 20 parts 10% hydroxyethyl cellulose water soluble i 20
Department water
60 parts or more of the heat-sensitive recording material (a
), (b).

(C) was printed at high speed (printing speed: 0.94 m5ec, applied voltage: 16 V, 18 V, 20 V) using a G-111 prototype facsimile machine (manufactured by Ricoh Co., Ltd.), and the color density was determined using the Macbeth densitometer ratio D-514. (manufactured by Macbeth, USA).

The results are shown in Table-1. In addition, after leaving the above printed matter (printing speed 20.94 m5ec, applied voltage: 20 V) for one week, the density of the colored part was measured again using a Macbeth densitometer RD-5.
Measured at 4. In addition, white powder phenomenon in the colored area was also observed at that time. The results are shown in Table-2.

As is clear from Tables 1 and 2 below, the heat-sensitive recording material of the present invention has excellent color development during high-speed recording and is a heat-sensitive recording material with extremely stable colored images. I understand.
(, -Patent applicant Ricoh Co., Ltd. Patent attorney Toshiaki Ikeura

Claims (1)

[Claims] (1) A thermosensitive recording characterized by having a thermosensitive coloring layer containing at least one leuco dye and a phenolic substance represented by the following general formula (1) as a color developer for developing the leuco dye. material. and represents an integer from 1 to 4, and "When multiple substituents R and R' are bonded to the naphthalene nucleus, those substituents R and R' may be the same or different. )