JPS58222886A - Heat-sensitive recording sheet - Google Patents

Abstract

PURPOSE:To provide a heat-sensitive recording sheet excellent in color producing property at the time of high speed recording and stability of a color image, by a method wherein a heat-sensitive color producing layer comprising a leuco dye and a specified phenolic substance is provided. CONSTITUTION:The heat-sensitive color producing layer comprising at least one leuco dye and a phenolic substance of formula I (wherein X is a lower alkyl and/or halogen; n is 0-3) is provided on a base to obtain the heat-sensitive recording sheet. Accordingly, a heat-sensitive recording sheet having a high sensitivity can be produced without requiring any sensitizer or any melting point lowering agent, and since the sheet is particularly excellent in response to heat, a clear image of high color density can be obtained even in high-speed high- density recording. In addition, the sheet is free from such troubles as adhesion of scum to a thermal head or sticking, and is excellent in adaptability to recording.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat-sensitive recording sheet, and particularly to a heat-sensitive recording sheet 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 anti-EE.

Compared to other recording materials, this heat-sensitive recording sheet allows recording to be obtained in a relatively short period of time without the need for complicated processes such as phenomenon and fixing, and there is no generation of noise75; Due to its low cost and other advantages, it is widely used not only for copying books and documents, but also as a recording material for various information and measuring instruments such as electronic computers, facsimiles, telex machines, and 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, such heat-sensitive recording notebooks for high-speed recording are 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, etc., heat-melting substances with low melting points such as various waxes, fatty acid amides, alkylenyls, substituted hyphenyl 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 not only is it not possible to obtain sufficient thermal responsiveness to minute amounts of heat with short pulses. , because 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.
Furthermore, even under storage conditions of high temperature or high humidity, background coloring (fogging) often occurs over time, and the contrast of recorded images often deteriorates.

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.
Color-forming colorless dyes with structures such as lactones, lactams, and spiropyrans used in heat-sensitive recording sheets usually have a high melting point of 160 to 240°C, so they are suitable for high-speed recording without adding sensitizers or melting point depressants. In order to obtain heat-sensitive recording sheets, phenolic substances have been used as color developers, which have a low melting point and have a high ability to color colorless dyes.

Regarding the color developer for phenols,
A large number of substances have been described in various documents including Publication No. 039, among which 2,2-bis(4'-hydroxyphenyl)propane (bisphenol A melting point 15
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-su7thol (melting point 119-122°C) are used, as
・I Ha 11 liver 7 sounds 1. Not only does it turn dark brown, but it also has a strong 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, Japanese Patent Application Publication No. 1983. - In Publication No. 144193 p-
It is described that lower alkyl esters or benzyl esters of hydroxybenzoic acid are easy to synthesize and can be used to make highly sensitive heat-sensitive recording sheets, but this material suffers from rapid natural discoloration of the color-forming portion and also It has the disadvantage that crystals of the phenolic substance precipitate in the coloring area (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.

The inventors of the present invention have conducted various studies to improve these many drawbacks, and as a result, they have found a practical solution by using a phenolic substance represented by the following formula (summer) as a color developer. It has been discovered that a heat-sensitive recording sheet for high-speed recording having extremely excellent properties can be obtained, leading to the completion of the present invention.

That is, the present invention is a heat-sensitive recording sheet characterized in that a heat-sensitive coloring layer containing at least one leuco dye and a phenolic substance represented by the following general formula (1) is provided on a support.

(In the formula, X represents a lower alkyl group and/or a halogen atom, n is O~3, and when multiple substituents X are bonded to the benzene nucleus, the substituents X are the same or different. (The lower alkyl group is usually preferably one having 1 to 4 carbon atoms, and the halogen atom includes chlorine, fluorine, etc.) According to the present invention, the above general formula By using the phenolic substance (1), a heat-sensitive recording sheet exhibiting the excellent properties listed below can be obtained.

(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 strobe 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, phenothiazine-based, auramine-based, and spiropyran-based dyes, which are generally known as colorless to light-colored colorless dyes, and are not particularly limited. Examples include, but are not limited to, crystal violet lactone 3-diethylamino-6-methyl-7-anilinofluorane 3-(N-ethyl-p-)luidino)-6-methyl-7
-anilinofluorane 3-gelamino-6-methyl-7-(ortho.

para-dimethylanilino)fluoran 3-pyrrolidino-6-methyl-7-anilinofluoran 3-piperidino-6-methyl-7-anilinofluoran 3-(N-cyclohexyl-N-methylamine)- 6-
#f-7-anirite fluorane 3-diethylamine-
7-(orthochloroanilino)fluoran 3-diethylamino-7-(meta-trifluoro-methylanilino)fluoran 1 3-diethylamino-6-methyl-7-chlorofluoran 3-diethylamino-6-methylfluoran 3-cyclo Hexylamino-6-chlorofluorane and the like.

Further, the compound of formula (1) used in the present invention is preferably used in an amount of 1 to 6 times the amount of the leuco dye.

Specific examples of the phenolic substance represented by the general formula (1) include those shown below.

H3 It should be noted that in the heat-sensitive coloring layer of the present invention, various commonly used binders may be appropriately used for bonding and supporting on the support, such as polyvinyl alcohol, methoxy cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, Binders are water-soluble such as polyviterpyrrolidone, polyacrylamide, polyacrylic acid, starch, gelatin, etc., or water-based emulsions such as polystyrene, vinyl chloride-vinyl acetate copolymer, polybutyl methacrylate, etc. It can be used as

In addition, if necessary, conventional auxiliary additives such as fine powders such as calcium carbonate, silica, alumina, magnesia, talc, titania, barium sulfate, and aluminum stearate may be added to the heat-sensitive coloring layer to develop color. Image clarity 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.

Example 1 Mixtures having the following compositions were separately pulverized and dispersed for two days using a magnetic ball mill to obtain CA1 liquid [B] and liquid [C].
] A solution was prepared.

(A) Liquid fluoran 10% hydroquine ethyl cellulose aqueous solution 20 //
water 60
...CB] Liquid 4-benzylmercaptophenol 20 Parts by weight 10% hydroxyethyl cellulose aqueous solution 20
tt water
60 [C') Liquid calcium carbonate 20 parts by weight 5% methyl cellulose aqueous solution 2 o Using the liquids A'l to [c] obtained as above,
A heat-sensitive coloring layer liquid with the following composition was prepared, and the standard basis weight was 5°17m.
2 commercially available high-quality paper with a dry coating amount of 4 ~! M'/m2 is selected using a wire bar, applied and dried, and then the smoothness of the surface of the heat-sensitive coloring layer is 500 to 6oof in Bekk smoothness.
'a, b, h, ka' in 'J'7F-#fik-j L
% EE'': A thermosensitive recording sheet (a) of the invention was produced.

Thermosensitive coloring layer liquid [A] tL 10 parts by weight [13) Liquid 3Q tt
0) Solution 3Q u Isobutylene-maleic anhydride copolymer 1ol 1020% alkaline aqueous solution Example 2 Thermal recording was carried out in the same manner as in Example 1 except that the following CI)) solution was used in place of the CB) solution in the example. Sheet (b)
made.

[1)) Liquid 10% hydroxyethyl cellulose aqueous solution 20
/l water
60 Comparative Example Thermal recording sheet (C) was prepared in the same manner as in Example except that the following liquid (E) was used instead of liquid [B] in Example 1.
made.

[E] Liquid bisphenol A 20 parts by weight 10% hydroxyethyl cellulose aqueous solution 20 parts by weight Water
(Thermal recording sheets obtained as described above in Q11) (a) to (C) were printed at high speed using a G-1 facsimile machine (manufactured by Ricoh Co., Ltd.) (printing speed: Q, 94 m5e)
c. Applied voltage: 16V.

Macbeth ILI)
-514. The results are shown in Table-1.

Table 1 As is clear from Table 1, the heat-sensitive recording sheet of the present invention has extremely excellent color development during high-speed recording.

Patent applicant Ricoh Co., Ltd. Agent: Patent Attorney Toshiaki Ikeura

Claims (1)

[Claims] (1) A heat-sensitive recording sheet characterized in that a heat-sensitive coloring layer containing at least one type of leuco dye and a phenolic substance represented by the following general formula (+) is provided on a support. (In the formula, X represents a lower alkyl group and/or a halogen atom, n is 0 to 3, and when multiple substituents X are bonded to the benzene nucleus, the substituents X are the same or different. )