JPS58166097A - Heat-sensitive recording material - Google Patents

Abstract

PURPOSE:To improve water resistance, by using a specified phenol compound as a developer for a leuco dye. CONSTITUTION:As the developer for a normally colorless or light-colored leuco dye of e.g., triphenylmethane or fluoran series, a phenol compound of formula I (wherein R<1> and R<2> are each a 1-3C alkyl group), e.g., bis (2,5-dimethyl-4- hydroxyphenyl) sulfide, wherein R<1> and R<2> are methyl, is compounded to form a heat-sensitive color forming layer. In general, a dye solution containing the leuco dye, a developer solution containing the phenol compound, and a filler solution are prepared, mixed, applied on paper as a support, and dried. Then calendering is performed to smooth the surface. The obtained heat-sensitive recording sheet has an excellent water resistance and gives stable recorded image.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat-sensitive recording material, and more particularly to a heat-sensitive recording material with excellent water resistance of colored images.

Heat-sensitive recording sheets that utilize a heated color-forming reaction between normally colorless or light-colored colorless dyes (leuco dyes) and phenols or organic acids are disclosed in Japanese Patent Publication No. 43-4160 and Japanese Patent Publication No. 45.
-14039, Japanese Unexamined Patent Publication No. 48-27736, etc., and has been widely put into practical use. In general, heat-sensitive recording sheets are produced by pulverizing and dispersing a leuco dye and a color developer such as a phenolic substance into fine particles, and then mixing the two to form a binder and a color developer.
A coating solution obtained by adding fillers, sensitivity improvers, lubricants and other auxiliaries is coated onto a support such as paper or film.
Color recording is obtained through an instantaneous chemical reaction caused by heating. A thermal printer or the like with a built-in thermal head is used to heat such a heat-sensitive wiring sheet to develop color. Compared to other recording materials, such recording sheets can produce records in a relatively short time without complicated processes such as development and fixing, do not generate noise, and are relatively inexpensive. Due to these 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, telex machines, and medical measuring instruments.

However, if heat-sensitive recording sheets made of such combinations of leuco dyes and phenolic substances are exposed to water or immersed in water, the image area will fade and the sheet will lose its value as a record. . This phenomenon is thought to be due to the gradual dissolution of phenolic substances into water, which causes the leuco dye, which had been once colored, to return to its original colorless state.

Therefore, if a phenolic substance that has a strong binding force with leuco dyes and low solubility in water is used, it can be expected that the image area will not disappear even if it is splashed with water or immersed in water. There is nothing known to be satisfied. On the other hand, the fields of use of thermal recording sheets that strongly require water resistance include ticket tickets using thermal paper, thermal paper for medical measuring instruments, and thermal labels for bar codes for POS at A&H stores and the like.

In such areas of use, thermal paper is exposed to water,
There is a high possibility that it will be immersed in water, and conventional thermal paper has the drawback that the image will fade.

As a conventional thermal paper with improved water resistance.

It has been proposed that a water-soluble polymer overcoat layer is provided on the heat-sensitive coloring layer, but this one is.

Since the overcoat layer impedes heat conduction, the thermal sensitivity is poor, and a coating process for the overcoat layer is required, resulting in high costs. Therefore, in order to obtain a heat-sensitive recording sheet that does not require an overcoat layer and has good water resistance, it is necessary to develop a phenolic substance that has a strong binding force with leuco dyes and has low solubility in water.

As a result of extensive research into the development of heat-sensitive recording materials with improved water resistance, the present inventors have discovered that heat-sensitive recording materials containing at least one type of leuco dye and a phenolic substance represented by the following general formula (1). They have discovered that a sheet is optimal for this purpose, and have completed the present invention.

(In the formula, Bl and R2 represent an alkyl group having 1 to 3 carbon atoms.) The phenolic substance used in the present invention acts as a color developer for the leuco dye, and specific examples thereof include the following. can.

The normally colorless to light-colored leuco dye used in the present invention includes various conventionally known leuco dyes, including, but not limited to, triphenylmethane, fluoran, phenothiazine, auramine, and spiropyran dyes. is preferably applied. Specific examples of these leuco dyes are shown below.

3.3-bis(p-dimethylaminophenyl)-phthalide 3.3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide (also known as crystal violet lactone) 3.3-bis(p-dimethylamino phenyl)-6-dibutylaminophenyl 3.3-bis(p-dimethylaminophenyl)-6-chlorophthalide 3.3-bis(p-dibutylaminophenyl)phthalide 3-cyclohexylamino-6-chlorofluorane 3-( N,N-diethylamino)-5-methyl-7-(
N,N-dibenzylamino)fluoran 3-dimethylamino-5,7-dimethylfluoran 3-diethylamino-7-methylfluoran 3-diethylamine-7,8-benzfluoran 3-diethylamino-6-methyl- 7-Chlorfluorane ' 3-pyrrolidino-6-methyl-7-anilinofluorane 2- (N -(3'-trifluoromethylphenyl)
amino)-6-dinithylaminofluorane 2-(a,6
-bis(diethylamino)-9-(0-chloroanilino)xantylbenzoic acid lactam) 3-diethylamino-? -(o-chloroanilino)fluoran 3-dibutylamino-7-(0-chloroanilino)fluoran 3-N-methyl-N-amylamino-6-methyl-7-
Anilinofluorane 3-N-methyl-N-cyclohexylamino-6-methyl-7-anilinofluorane a -(2'-hydroxy-4'-dimethylaminophenyl) -3-(2'-methoxy-5 '-Chlorphenyl)phthalide a -(2'-hydroxy-4'-dimethylaminophenyl) -3-(2'-methoxy-57-nitophenyl)phthalide a (2/-hydroxy-4'-diethylaminophenyl) -3-(2'-methoxy-5'-methylphenyl)phthalide a, (2/-methoxy-4'-dimethylaminophenyl)-3-(,2'-hydroxy-4'-chloro-
5'-Methylphenyl) Lid IJ l' Note that in the thermosensitive coloring layer of the present invention, a conventional binder may be used as appropriate for bonding and supporting on the support, such as methylcellulose, hydroxyethylcellulose, carboxylic Methylcellulose, polyvinyl alcohol, carboxyl-modified polyvinyl alcohol, polyvinylpyrrolidone, polyacrylamide, polyacrylic acid, starch and its derivatives, casein, gelatin, alkali 1) salt of styrene-maleic anhydride copolymer, iso(or diiso)butylene - water-soluble ones such as alkali salts of maleic anhydride copolymers, or polystyrene, polyvinyl acetate, vinyl chloride/vinyl acetate copolymers, polyurethanes, polyacrylic esters, styrene/butadiene/acrylic copolymers, Mention may be made of aqueous emulsions such as polyester.

Fillers, thermofusible substances, etc. can be added to the heat-sensitive coloring layer as necessary. Examples of fillers include calcium carbonate, magnesium carbonate, alumina, silica, talc, barium sulfate, and magnesium hydroxide. , aluminum hydroxide, aluminum stearate, styrene resin,
Examples include fluororesin, urea-formalin resin, and the like. Furthermore, examples of thermofusible substances include the following.

Animal waxes such as beeswax and shellac wax, vegetable waxes such as carnauba wax, mineral waxes such as montan wax, petroleum waxes such as paraffin wax and microcrystalline wax, polyhydric alcohol esters of higher fatty acids, and higher amides. Synthesis of higher amine fatty acid and amine condensates, aromatic and amine condensates, synthetic paraffins, chlorinated paraffins, higher linear glycols, dialkyl 3,4-epoxy-hexahydrophthalates, metal salts of higher fatty acids, etc. Waxy substance.

The heat-sensitive recording material of the present invention is produced by applying a coating solution for forming a heat-sensitive layer containing the above-mentioned components onto a suitable support such as paper, synthetic paper, or glass film, and drying it. It is used as an excellent heat-sensitive recording sheet.

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

Example 1 A mixture having the following composition was separately pulverized and dispersed for two days using a magnetic ball mill to obtain liquid (A), liquid [B], and (
0) A solution was prepared.

(A) Liquid 10% hydroxyethyl cellulose aqueous solution 20//
water 6
0 (B) Liquid bis(2,5-dimethyl-4-hydroxyne 2' O
filtn enyl) sulfide lO% hydroxyethyl cellulose water m solution 2o parts by weight water
60 [C] Liquid calcium carbonate 20 parts by weight 5% methylcellulose aqueous solution 20 //Water
60 Using the solutions (A) to [0'E obtained as described above, a heat-sensitive coloring layer solution having the following composition was prepared, and a dry coating amount of 4 to 4 was applied to commercially available high-quality paper with a standard basis weight of 50 g/m''. 5 g/m" with a wire bar, and dried. Next, the heat-sensitive coloring layer surface was calendered so that the Bekk smoothness was 500 to 600 seconds. I made a).

[Thermosensitive coloring layer liquid]

(A) Liquid lO weight part CB
)Liquid 30〃 (C)Liquid 30" Example 2 A thermosensitive recording sheet (b
)made.

[D゛]Liquid 10% hydroxyethylcellulose aqueous solution 20
water
60,.

Comparative Example 1 A thermosensitive recording sheet (
C) was made.

[E] Liquid bisphenol A 20 parts by weight 10
% hydroxyethylcellulose aqueous solution 20〃Water
60
Comparative Example 2 A thermosensitive recording sheet (d) was prepared in the same manner as in Example 1 except that the following CF'l liquid was used instead of the CB'l liquid in Example 1.

[F] Liquid P-Hydroxybenzoic acid benzyl ester 20 parts by weight 10% hydroxyethylcellulose aqueous solution 2011 Water 60
〃Thermal recording sheet obtained as above) (a) ~
(d) was subjected to a pressure of 2 KP using a thermal gradient tester (manufactured by Toyo Seiki).

Printing was carried out at 15 Orr with a contact time of 1 second.

The heat-sensitive recording sheets of (,) to (d) were cut out into 4 square square pieces centering on the printed area, and each cut was immersed in a 1001 beaker filled with tap water for 24 hours.

After taking it out, dry it and change the density of the painted area to Macbeth RD-
514 and compared with the concentration before the test, Table 1 was created.

Table 1 As is clear from Table 1, the heat-sensitive recording sheet of the present invention is a heat-sensitive recording sheet with excellent water resistance and stable images.

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

Claims (1)

[Claims] (1) A thermosensitive coloring layer containing a leuco dye and a phenolic substance represented by the general formula (wherein Bl and R2 represent an alkyl group having 1 to 3 carbon atoms) was formed on a support. A heat-sensitive recording material characterized by: