JPS5914989A - Heat sensitive recording material - Google Patents

Abstract

PURPOSE:To provide a heat sensitive recording material especially excellent in color formability at the time of high speed recording and image stability, obtained by containing a specific phosphorous ester compound in a heat sensitive color forming layer as a color coupler along with a leuco dye. CONSTITUTION:One kind or more leuco dye (e.g., Crystal Violet lactone), a phosphorous ester compound shown by formula (wherein Ar is an aromatic ring) [e.g., tris-(bisphenol A)-phosphite], a binder such as hydroxyethyl cellulose and, according to necessity, auxiliary additives such as calcium carbonate are compounded to obtain a composition which is, in turn, applied to a support such as paper to be dried thereon to form a heat sensitive color forming layer. By this method, an objective recording material is obtained.

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.

In general, heat-sensitive recording sheets consist of a heat-sensitive color-forming layer containing a color-forming colorless dye and a color developer such as a phenolic substance on a support such as paper or film. Color recording is obtained by reaction.

Compared to other recording materials, this heat-sensitive recording sheet can produce records in a relatively short time without undergoing complicated processes such as phenomenon and fixing, does not generate noise, and is relatively inexpensive. Due to certain advantages, it is widely used not only for copying books, documents, etc., but also as a recording material for various information and measuring instruments such as electronic computers, facsimiles, and telex medical measuring instruments.

However, in recent years, with the development of society, there has been a growing demand for faster recording, so there is a strong desire for faster recording devices themselves and for the development of recording materials that can meet this demand.

Conventionally, various heat-sensitive recording sheets for high-speed recording have been disclosed in Japanese Patent Application Laid-open No. 53-39139 and Japanese Patent Application Laid-Open No. 53-26139.
No. 1, JP-A-53-5636, JP-A-53-1
As disclosed in Japanese Patent No. 1036, heat-melting substances with low melting points such as various waxes, fatty acid amides, alkylated biphenyls, substituted biphenyl alkalis, coumarin compounds, and diphenylamines are used as sensitizers or melting point depressants. It has been proposed to add it to a heat-sensitive coloring layer.

This method of adding a sensitizer requires first melting the sensitizer prior to the color development reaction, so in high-speed recording, it is difficult to obtain sufficient thermal responsiveness to minute amounts of heat in a short period of time. However, since the fusible substance in the coloring layer melts, problems such as adhesion of residue on the thermal head, bleeding, trailing, and ghosting are likely to occur. Even under these storage conditions, background coloration (fogging) occurred over time, and the contrast of recorded images often deteriorated.

Therefore, it is desirable to have a heat-sensitive recording sheet for high-speed recording without the addition of such an increaser or melting point depressant.
The melting point of color-forming colorless dyes (leuco dyes) with structures such as lactones, lactams, and spiropyrans used in heat-sensitive recording sheets is usually as high as 160 to 240°C. In order to obtain heat-sensitive recording sheets suitable for recording, phenolic substances have been used as color developers that have a low melting point and a high ability to color colorless dyes.

Regarding color developers for phenols, Japanese Patent Publication No. 45-140
A large number of substances have been described in various documents, including Publication No.
6 to 158°C) is frequently used from the viewpoint of quality stability, price, and ease of acquisition.

However, this bisphenol A has the drawback of a high thermal coloring temperature.

In contrast, phenolic substances with low melting points, such as 4-
Tertiary-butylphenol (melting point 94-99°C),
When monophenols such as α-naphthol (melting point 95-96°C) and β-naphthol (melting point 119-122°C) are used, the storage stability and stability of the heat-sensitive recording sheet are poor, and the background color gradually changes even at room temperature. Not only does it develop color, but it also has a strong so-called phenol odor, making it impractical.

In addition, 2,2-bis(4'-hydroxyphenyl) normal hexane (melting point 99-103°C) is used in Japanese Patent Publication No. 54-12819, and 1,1-bis(4'- -Hydroxyphenyl) alkanes (alkanes have 3 to 13 carbon atoms) each have a low melting point and can be used to produce heat-sensitive recording sheets with good stability and color development, but these substances are difficult to synthesize. There is a problem with availability.

Furthermore, JP-A-56-144193 describes that lower alkyl esters or benzyl esters of p-hydroxybenzoic acid are easy to synthesize and can produce highly sensitive heat-sensitive recording sheets. However, it has the disadvantage that the coloring part undergoes rapid natural discoloration, and crystals of the phenolic substance still precipitate in the coloring part (so-called white powder phenomenon).

As mentioned above, among the color developers that can be used practically and industrially, there are currently few that have been found that produce clear and high-density colored images during high-speed recording, and that produce stable colored images. be.

As a result of various studies aimed at improving these many drawbacks, the present inventor has developed an extremely excellent practical solution by using a phenolic substance represented by the following formula (1) as a color developer. It was discovered that a heat-sensitive recording sheet for high-speed recording having the following characteristics could be obtained, and the present invention was completed.

That is, according to the present invention, a color developer comprising at least one leuco dye and at least one phosphite compound represented by the general formula % (wherein Ar represents an aromatic ring). Provided is a heat-sensitive recording material having a heat-sensitive coloring layer comprising:

In the phosphite compound represented by the above general formula, the aromatic ring Ar is a benzene ring, two benzene rings directly bonded, or a carbon atom or a heteroatom, such as a sulfur atom, a nitrogen atom, or an oxygen atom. Those bonded through atoms, and naphthalene rings can be mentioned,
These aromatic rings may be substituted with a substituent such as a lower alkyl group or a halogen atom.

Specific examples of the phosphite compound used as a color developer in the present invention are shown below.

Tris-(p-hydroxyphenyl)phosphite 6-1-IJsu-(m-hyroxyphenyl)-phosphite 1-IJsusu-2-methyl-4-hydroxyethyl)
-Phosphite tris-(P-hyperoxybenzophenone)-phosphite tris-(methylenebisphenol)-phosphite tris-(bisphenol-A)-phosphite tris-(p-oxybenzophenone)-phosphite 1-IJ Su(p-bi10xypiphenylthioether)-phosphite tris-(bisphenol-5)-phosphite tris-(p-hydroxybiphenylamine)-phosphite IJsu-(p-hydroxybiphenyl ether)- Phosphite Tris-(4-hydroxynaphthane)-phosphite The phosphite compound used as a color developer in the present invention is 1 to 50 parts by weight, preferably 3 to 10 parts by weight, per 1 part by weight of the leuco dye. If necessary, it can be used in combination with other color developers such as conventional bisphenol A.

By using the phosphite compound of the present invention, a heat-sensitive recording sheet can be obtained that exhibits the excellent properties listed below.

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

(2) There are no problems such as adhesion of residue or sticking to the thermal head, and the recording suitability is excellent.

(3) By coating thin base paper or film, excellent copying paper for infrared and Stroze flash type thermal copying machines can be obtained.

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

(5) It is easy to synthesize, can be obtained in high yield and purity, and can be produced at relatively low cost.

Next, the leuco dyes used in the present invention include triphenylmethane-based, fluoran-based, fetchazidi/, auramine-based, and spiropyran-based dyes, which are generally known as colorless to light-colored colorless dyes, and are particularly limited. Examples include, but are not limited to, CrystalnoS iolet lactone 3-diethylamino-6-methyl-7-anilinofluorane 3-(N-ethyl-p-)luidino)-6-methyl-7
-anilinofluorane 3-gelamino-6-methyl-7-(ortho.

・ξlargemethylanilino)fluoran 3-pyrrolidino-6-methyl-7-anilinofluoran 3-giberituno-6-methyl-7-anilinof 9-luoran 3-(N-cyclohexyl-N-methylamino )-6-
Methyl-7-anilinofluorane 3-diethylamine-
7-(orthochloroanilino)fluoran 3--)ethylamino-7-(meta-trifluoromethylanilino)fluoran 3-diethylamino-6-methyl-7-chlorofluoran 3-diethylamino-6-methylfluoran 3-cyclohexylamino-6-chlorofluorane and the like.

It should be noted that in the heat-sensitive coloring layer of the present invention, various conventional binders may be appropriately used for bonding and supporting on the support, such as polyvinyl alcohol, methoxycellulose, hydroxyethylcellulose, carboxymethylcellulose, polyvinylpyrroli The binder may be water-soluble, such as polyester, polyacrylamide, polyacrylic acid, starch, gelatin, etc., or an aqueous emulsion, such as polystyrene, vinyl chloride-vinyl acetate copolymer, polybutyl methacrylate, etc. It can be used as

-1. If necessary, conventional auxiliary additives such as fine powders of calcium carbonate, silica, alumina, magnesia, talc, titania, barium sulfate, and aluminum stearate may be added to the heat-sensitive coloring layer. , the clarity of colored images can be improved.

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

Next, the present invention will be explained in more detail with reference to Examples. Note that all parts and percentages shown below are based on weight.

Example 1 Solutions A and B having the following component compositions were prepared.

Part A 10% aqueous solution of hydroxyethyl cellulose 40 parts water
120 parts B solution (1): (comparative product) 10% aqueous ti of hydroxyethyl cellulose
2081+Wed
60 parts Solution B (2): (Invention product 1) 10% aqueous solution of hydroxyethyl cellulose 20 parts water
6
0 parts Solution B (3): (Invention product 2) 10% aqueous solution of hydroxyethyl cellulose 20 parts water

60 parts After dispersing each of the above solutions in a Dahl mill for 2 days, mix 5 parts of Part A with 15 parts of Part B (1), and further add 8 parts of a 20% aqueous solution of oxidized starch. Mix and prepare a coating liquid for heat-sensitive recording. Further, liquid A and liquid B (2) were mixed in the same ratio, and liquid A and liquid B (3) were still mixed to prepare a coating liquid.

Next, on one side of a high-quality paper with a standard basis weight of 52 f/m2, the above-mentioned three types of coating liquids were applied with a dry adhesion of 417 m2 and a smoothness of 130.
A heat-sensitive recording sheet was prepared by applying the mixture for ~200 seconds, and each recording sheet was evaluated.

The thermal sensitivity of the recording paper was evaluated using a facsimile simulator by comparing the color density when a thermal head was brought into contact with the recording sheet with a constant applied voltage applied for a constant application time. In addition, regarding storage stability, 40℃, humidity 90℃
%RFI atmosphere was prepared and each recording paper was compared in terms of the degree of change in image area density and non-image area density when left for 24 hours. The results are shown in the table below.

Table 1 From the results shown in this table, it can be seen that both products 1 and 2 of the present invention have improved color development heat sensitivity and excellent preservability compared to conventional products.

Example 2 In the coating liquid consisting of liquid A and B(2)I shown in Example 1, tris-(bisphenol-A) in liquid B(2)
)-A thermosensitive recording sheet was prepared in the same manner except that the phosphite shown below was used in place of the phosphite.

14- (1)) IJsusu-p-hyPoxyphenyl)-bosphite (2)) Lis-(p-hydroxybiphenyl)-'
Phosphite (3) Tris-(p-benzophenone)-
Phosphite (4)) IJ susu-p-hydroxybiphenylamine)
-Phosphite (5) Tris-(4-hydroxynaphthalene)-Posphite The heat-sensitive recording sheet obtained above also has good color development thermal sensitivity and storage stability, similar to the product of the present invention obtained in Example 1. did.

Patent applicant Ricoh Co., Ltd. Agent Patent Attorney Toshiaki Ikeura 15- 473-

Claims (1)

[Claims] (1) At least one leuco dye and a color developer consisting of at least one phosphite compound represented by the general formula % (where Ar represents an aromatic ring). A heat-sensitive recording material having a heat-sensitive coloring layer comprising: