JPH0351596B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to improvements in heat-sensitive recording materials containing leuco dyes as color formers. Thermosensitive recording materials generally have a thermosensitive coloring layer containing a thermochromic composition as a main component on a support such as paper, synthetic paper, or plastic film, and can be heated with a thermal head, thermal pen, laser beam, etc. By doing so, a colored image can be obtained. Compared to other recording materials, this type of recording material can produce records in a short time using relatively simple equipment without requiring complicated processes such as development and fixing, and generates less noise and pollutes the environment. , has advantages such as low cost, and is widely used in various fields such as computers, facsimile machines, ticket vending machines, labels, and recorders, in addition to being used for copying books and documents. Thermochromic compositions used in heat-sensitive recording materials generally consist of a color former and a color developer that causes the color former to develop color when heated. The color former may be a colorless or light-colored composition having a lactone, lactam or spiropyran ring. Leuco dyes are used, and acidic substances such as organic acids and phenolic substances are used as color developers. Recording materials that combine this color forming agent and color developer have the advantages that the resulting images have clear tones, high whiteness of the background, and have excellent weather resistance, and are widely used. ing. However, in recent years, as demand for heat-sensitive recording methods has increased as they have replaced other conventional recording methods, there has also been an increasing demand for improved quality of heat-sensitive recording materials used in this method. An object of the present invention is to improve the finger squeezing resistance and plasticizer resistance, which are disadvantages of conventional heat-sensitive recording materials that use leuco dyes as color formers. It is known among those skilled in the art that phenolic ranges and clays are slightly better than conventional phenolic substances in order to improve finger squeezing resistance and plasticizer resistance. Although it is known to have some effects, these effects are so weak that it has not been possible to obtain a heat-sensitive recording material of sufficient quality. In order to achieve the above object, the present inventors have conducted intensive research on electron-accepting compounds, and found that by using a specific compound as a color developer,
The inventors have now completed the present invention by discovering that a heat-sensitive recording material can be obtained which has excellent heat-sensitive color development ability, as well as excellent water resistance, light resistance, plasticizer resistance, and finger-squeezing resistance. That is, according to the present invention, in a heat-sensitive recording material in which a heat-sensitive color forming layer containing a leuco dye and a color developer for the leuco dye is provided on a support, the color developer has the general formula () (In the formula, R ₁ and R ₂ represent a hydrogen atom, a halogen, an alkyl group, an alkoxy group, a cyclohexyl group, or an aromatic group.) be done. In the compound represented by the general formula (), examples of the halogen included in the substituents R ₁ and R ₂ include chlorine and bromine, and examples of the alkyl group include carbon atoms such as methyl, ethyl, propyl, octyl, and dodecyl. Examples of the alkoxy group include those having 1 to 20 carbon atoms, such as methoxy, ethoxy, propoxy, octyloxy, dodecyloxy, etc., and aromatic groups include:
Examples include aryl groups such as phenyl, tolyl, xylyl, and pt-butylphenyl, and aralkyl groups such as benzyl and phenethyl. Specific examples of the compound represented by the general formula () of the present invention include those having the structures shown below. The amount of the compound represented by the general formula () used in the present invention is leuco dye 1 in the heat-sensitive coloring layer.
Usually 1 to 10 parts by weight, preferably 2 to 10 parts by weight
5 parts by weight are used. In the present invention, it is possible to use other commonly used color developer substances in combination if necessary, but in such a case, the color developer substance represented by the general formula () of the present invention has a total color developability. In the substance, the amount is 5% by weight or more, preferably 20 to 100% by weight or more. As the leuco dye used in the present invention, any dye can be used as long as it develops color when heated by the compound represented by the general formula () as a color developer, including triphenylmethane, fluoran, and phenothiazine. Leuco dyes such as auramine-based, auramine-based, and spiropyran-based leuco dyes are preferably used. Specific examples of these leuco dyes are shown below. As the leuco dye, the leuco forms of the various colorless or light-colored dyes shown below are usually used. (a) Leuco compound of triphenylmethane dye represented by the following general formula: (In the formula, R _X , R _Y and R _Z are hydrogen, hydroxyl group, halogen, alkyl group, nitro group, amino group, dialkylamino group, monoalkyl group, and allyl group.) Specific examples of the above leuco compounds are as follows. It is as follows. 3,3-bis(p-dimethylaminophenyl)-phthalide 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide (also known as crystal violet lactone) 3,3-bis(p- Dimethylaminophenyl)-6-diethylaminophthalide 3,3-bis(p-dimethylaminophenyl)-6-chlorophthalide 3,3-bis(p-dimethylaminophenyl)phthalide (b) Represented by the following general formula Leuco compounds of fluoran dyes: In the formula, R _X , R _Y and R _Z are the same as in (a) above. Specific examples of the above compounds are as follows. 3-cyclohekynylamino-6-chlorofluorane 3-(N,N-dimethylamino)-5-methyl-7-(N,N-dibenzylamino)fluoran 3-dimethylamino-5,7-dimethylfluoran 3-diethylamino-7-methylfluorane 3-diethylamino-7,8-benzfluorane (c) Leuco compounds of fluoran dyes: 3-diethylamino-6-methyl-7-chlorofluorane 3-pyrrolidino-6-methyl -7-anilinofluorane 2-{N-(3'-trifluoromethylphenyl)amino}-6-diethylaminofluorane 2-{3,6-bis(diethylamino)-9-
(o-chloroanilino)xantylbenzoic acid lactam} (d) Lactone compound represented by the following general formula: In the formula, R ₁ and R ₂ are hydrogen, lower alkyl group,
Substituted or unsubstituted alkyl group, substituted or unsubstituted phenyl group, cyanoethyl group, or β-
represents a halogenated ethyl group or R ₁ and
R ₂ is bonded to −(CH ₂ ) − ₄ , −(CH ₂ ) − ₅ or −(CH ₂
) _−2O− ( _CH2 ) ₋₂ , _R3 and _R4 are hydrogen,
Represents a lower alkyl group, an alkyl group, an amino group or a phenyl group, one of R ₃ and R ₄ is hydrogen, and X ₁ , X ₂ and X ₃ are hydrogen, a lower alkyl group, a lower alkoxy group, a halogen represents an atom, a halogenated methyl group, a nitro group, an amino group, or a substituted amino group, _X4 represents hydrogen, halogen, a lower alkyl group or a lower alkoxy group, and n represents 0 or an integer of 1 to 4. . Specific examples of the above compounds are as follows. 3-(2'-hydroxy-4'-dimethylaminophenyl)-3-(2'-methoxy-5'-chlorophenyl)phthalide 3-(2'-hydroxy-4'-dimethylaminophenyl)-3- (2'-methoxy-5'-nitrophenyl)phthalide 3-(2'-hydroxy-4'-diethylaminophenyl)-3-(2'-methoxy-5'-methylphenyl)phthalide 3-(2'-methoxy- 4'-dimethylaminophenyl)-3-(2'-hydroxy-4'-chloro-
5′-methylphenyl)phthalide. Next, various color developing substances can be used in combination with the above-mentioned compound of the present invention, and specific examples thereof are shown below. 4,4'-isopropylidene diphenol (bisphenol A), 4-t-butylphenol, 4
- phenylphenol, 4-hydroxydiphenoxide, α-naphthol, β-naphthol, methyl-4-hydroxybenzoate, 4-hydroxyacetophenone, 4-t-octylcatechol, 2,2'-hydroxydiphenyl, 2,2'-methylenebis(4-chlorophenol), 4,4'-
sec-butylidene diphenol, 4,4'-isopropylidene bis(2-methylphenol), 4,
4'-isopropylidene bis(2,6-dimethylphenol). As the binder for bonding and supporting the thermosensitive coloring layer on the support, various binders as shown below can be used. Water-soluble materials such as polyvinyl alcohol, methylcellulose, hydroxyethylcellulose, carboxymethylcellulose, polyvinylpyrrolidone, polyacrylamide, polyacrylic acid, starch, starch derivatives, gelatin, styrene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, etc. The binder may be a water-based emulsion such as polystyrene, vinyl chloride-vinyl acetate copolymer, polybutyl methacrylate, SBR latex, styrene-acrylic acid ester, and the like. In addition, if necessary, the heat-sensitive coloring layer may contain conventional auxiliary additives, such as inorganic pigments such as calcium carbonate, clay, talc, and zinc oxide to improve whitening and writing properties, and inorganic pigments to improve head matching properties. For this purpose, it is possible to add waxes such as polyethylene wax, paraffin wax, carnauba wax, montan wax, higher fatty acid metal salts, and also surfactants. Generally known methods can be used to obtain the heat-sensitive recording material of the present invention using the various heat-sensitive color forming layer forming components. That is, a chromogenic substance,
A color developing substance, a binder, a filler, and other additives are added alone or in a mixture except for the color forming substance, and added to an aqueous medium together with a protective colloid such as polyvinyl alcohol, a surfactant, etc., and then milled in a ball mill. Grind and disperse using a dispersing machine such as , attritor, or sand mill. Next, each dispersion liquid is mixed to prepare a heat-sensitive coloring layer coating liquid, and this is applied to paper, synthetic paper, etc.
Coat it on a support such as plastic film,
Manufactured by drying. Next, the present invention will be explained in more detail with reference to Examples. Note that all "parts" shown below are parts by weight. Example 1 The following ingredients were each ground using a ball mill.
Dispersions [A] to [C] were prepared by dispersing. [A] Liquid 3-(N-methyl-N-cyclohexylamino)-
6-Methyl-7-anilinofluorane 10 parts Hydroxyethyl cellulose 10% aqueous solution 5 parts Water 35 parts [B] Solution

[Formula] 30 parts 5% methyl cellulose aqueous solution 30 parts water 40 parts [C] Liquid titanium oxide 30 parts 10% polyvinyl alcohol aqueous solution 15 parts Water 105 parts Dispersion liquid prepared as above [A], [B],
[C] was uniformly mixed and stirred to obtain a thermosensitive color forming layer forming liquid of the present invention. Next, high-quality paper (basis weight: approx. 50g/
m ² ) The thermosensitive coloring layer forming liquid is applied onto the surface using a coating rod, dried to a solid content of approximately 5 g/m ² , and then calendered to a surface smoothness of 300 to 500 seconds. A heat-sensitive recording material was obtained. Example 2 A heat-sensitive recording material of the present invention was obtained in exactly the same manner as in Example 1, except that the following dispersion [D] was used instead of the dispersion [B] of Example 1. [D] Liquid

[Formula] 30 parts 5% methylcellulose aqueous solution 30 parts water 40 parts Example 3 This was carried out in exactly the same manner as in Example 1 except that the following dispersion [E] was used in place of the dispersion [B] of Example 1. A heat-sensitive recording material of the invention was obtained. [E] Liquid

[Formula] 30 parts Methyl cellulose 5% aqueous solution 30 parts Water 40 parts Comparative example 1 Comparative example was prepared in exactly the same manner as in Example 1 except that the following dispersion [F] was used instead of the dispersion [B] of Example 1. A heat-sensitive recording material was obtained. [F] Liquid bisphenol A 30 parts Methyl cellulose 5% aqueous solution 30 parts Water 40 parts Comparative example 2 Completely the same as Example 1 except that the following dispersion [G] was used instead of the dispersion [B] of Example 1. A heat-sensitive recording material for comparison was obtained. [G] Liquid 3,5-di-t-butylsalicylic acid zinc 30 parts Methyl cellulose 5% aqueous solution 30 parts Water 40 parts Printing was performed using a thermal head temperature of 130°C using a Macbeth densitometer (RD-514). The evaluation results are shown in Table-1.

【table】

[Table] As is clear from Table 1, the heat-sensitive recording material of the present invention has better image stability against plasticizers and oils than conventional products, and is also very superior with less color development in the background area. I understand that.

Claims (1)

[Scope of Claims] 1. A heat-sensitive recording material in which a heat-sensitive color forming layer containing a leuco dye and a color developer for the leuco dye is provided on a support, wherein the color developer has the general formula (In the formula, R ₁ and R ₂ represent a hydrogen atom, a halogen, an alkyl group, an alkoxy group, a cyclohexyl group, or an aromatic group.) A heat-sensitive recording material characterized by containing a compound represented by the following as a main component.