JPS58126191A - Heat-sensitive recording sheet - Google Patents

Abstract

PURPOSE:To obtain a heat-sensitive recording sheet with white ground texture and capable of giving high-density recording without chalking (or dusting) phenomenon by using a colorless or light-color leuco dye and a combination of two species of p-hydroxybenzoates as developing substances. CONSTITUTION:In a heat-sensitive recording sheet in which a heat-sensitive, color-forming layer composed primarily of a colorless or light-color leuco dye (e.g., Crystal violet lactone) and a developing agent is formed on a support, as the developing substance, a combination of a p-hydroxybenzoate derivative of formulaI(wherein R1 is a C1-C4 alkyl or benzyl) (e.g., methyl p-hydroxybenzoate) and a benzoate derivative of formula II (wherein R2 is a C1-C4 halogenated alkyl, a halogenated benzyl, or an alkylated benzyl with a C1-C3 alkyl) (e.g., a compound of formula III) is used. Thus, a heat-sensitive recording sheet with white ground texture and capable of giving high-density recordings without chalking (or dusting) in images can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat-sensitive recording sheet, and more specifically, it contains a leuco dye that is colorless or slightly pale at room temperature and an acidic substance that reacts with the leuco dye when heated to develop a color as a coloring component. This invention relates to an improvement in a heat-sensitive recording sheet having a heat-sensitive coloring layer provided on a support.

Recently, various recording sheets have been researched and developed and put into practical use in the information recording field in response to social demands such as the diversification and increase of information, resource conservation, and pollution-free technology.Among them, thermal recording sheets are (1) A colored image is recorded simply by heating, eliminating the need for a complicated development process; (2) It can be manufactured using a relatively simple and compact device;
Furthermore, the resulting recording sheet is easy to handle and maintenance costs are low; (3) paper is often used as a support; in this case, not only is the support cost low; Because of its advantages, such as the feel of the recorded recording sheet, which is similar to that of plain paper, it is useful in the fields of computer output, printers such as calculators, recorders for medical measurement, low and high speed facsimile IJ, automatic ticket vending machines, thermal copying, etc. It is widely used in

The heat-sensitive recording sheet is manufactured by coating and drying a heat-sensitive coloring layer liquid containing a coloring component that can cause a coloring reaction when heated, on a support such as ordinary paper, synthetic paper, or a synthetic resin film. A colored image is recorded on the heat-sensitive recording sheet thus obtained by heating it with a thermal pen or a thermal head. Conventional examples of such heat-sensitive recording sheets include, for example, the heat-sensitive recording sheet disclosed in Japanese Patent Publication No. 43-4160 or Japanese Patent Publication No. 45-14039; Responsiveness was low, and sufficient color density could not be obtained during high-speed recording, and non-printed areas developed color (called ghosting), greatly impairing sharpness. In addition, when recording by heating a thermosensitive recording sheet, the components in the thermosensitive coloring layer melt and stick to the thermal head or thermal pen (resistance adhesion), causing inconvenience in paper feeding and causing sticking phenomenon. This is extremely important when considering the quality of heat-sensitive recording sheets.

As a method for improving the above-mentioned drawbacks of conventional heat-sensitive recording sheets, for example, Japanese Patent Application Laid-open No. 19231/1983 discloses a method of incorporating waxes with a melting point of 40 to 100° C. into a heat-sensitive coloring layer to improve thermal responsiveness. In addition, Japanese Patent Publication No. 51-27599 describes a method of using a fatty acid amide and a petroleum wax together in a heat-sensitive coloring layer to improve thermal response and dust adhesion, but neither method is sufficient. It is not an improvement method, but a method for improving thermal response, especially during high-speed recording.
Further improvement is desired in head matching properties such as residual heat color development in non-printing areas and dregs adhesion.

As a result of various studies in view of the current situation, the present inventors found that the above-mentioned drawbacks could be almost solved by using P-oxybenzoic acid ester as a color developing substance, and filed an application with −!σa+f).

However, when the above-mentioned P-oxybenzoic acid is used, there is a problem that a phenomenon in which white powder is blown on the surface of the colored image (hereinafter referred to as ``powdering'') occurs over time after color development, resulting in a decrease in density. As a result of intensive research to solve this problem, it was discovered that the above problem could be solved by limiting the number of P-oxybenzoic acid ester derivatives and using a combination of two or more types.The present invention has been made. I was able to complete it.

That is, the present invention provides a heat-sensitive recording sheet having a structure in which a heat-sensitive color-forming layer containing as main components a normally colorless or slightly light-colored leuco dye and a color-developing substance for the leuco dye is formed on a support. The following general formula (
A heat-sensitive recording sheet characterized in that at least one type of P-oxybenzoic acid derivative represented by 1) and at least one type of P-oxybenzoic acid ester derivative represented by the general formula (In) are used together. It provides:

General formula (1) (In the formula, %R1 is an alkyl group having 1 to 4 carbon atoms or a benzyl group) General formula (I[) (In the formula, %R2 is a halogenated alkyl group having 1 to 4 carbon atoms,
The P-oxybenzoic acid ester derivative represented by the general formula (1) used as one component of the color developing substance in the present invention has a melting point of is 60 to 120°C, and has a high color developing ability, so it has a higher thermal reaction capacity than conventional color developing substances such as 4,4-isopropylidenediphenol and 4,4'-butylidenediphenol. (high recording density) and excellent uniformity of colored images. In addition, the general formula (
P-oxybenzoic acid ester represented by If) also has almost the same properties as those of general formula (1) when used alone, but when used in combination with those of general formula (1) and (II), , it is possible to prevent powdering of colored images.

As for powder blowing, analysis results have shown that it is recrystallized color developing substance, but general formula (1) and (
It is believed that when compounds with similar structures such as the compound II) are used in combination, crystallization is hindered and powdering is prevented.

Next, to explain the present invention in further detail, as a specific example of the P-oxybenzoate ester represented by the general formula (1) among the color developing substances, for example, methyl P-oxybenzoate (m, p, t25 ~
128℃) Ethyl P-oxybenzoate (m, p
, 116-118℃) P-oxybenzoic acid n-tetrapyrr (m, p, 96-98℃) P-, t* Isopcepyr cybenzoate (m, p, 84-86℃) P-, t
$ Isobutyl benzoate (m, p, 75-77
°C) Benzyl P-oxybenzoate (m, p, 11
1'C) etc. can be exemplified. On the other hand, in the P-oxybenzoic acid ester represented by the general formula (It), the halogen contained in the substituent R2 is chlorine, and the alkyl group of the alkylated benzyl group is
) can be exemplified as follows.

The combination of the compounds of general formula (1) and (m) is arbitrary, and any combination is effective against powder blowing, but for example, a great effect can be obtained when the following combination is used.

In the present invention, the color developing substance consisting of the above combination is generally used in an amount of 1 to 10 parts by weight per 1 part by weight of the leuco dye described below.
It is used in parts by weight, preferably in the range of 2 to 6 parts by weight. Further, the general formula (n
) weight ratio of color developer used ((n) / (1) '
) is preferably set to 0.1 to 5, particularly preferably 02 to 2. In addition, in the present invention, it is possible to use other conventional color developing substances in combination as necessary, but in such a case, the color developing substance of the general formula (II) selected in the present invention is In the sexual substance, the proportion is 5% by weight or more, preferably 10 to 50% by weight or more.

In addition, the leuco dye contained in the thermosensitive coloring layer is as follows:
Various products normally used in this type of field can be used, but in particular, 11 triphenylmethane, fluoran, phenothiazine, auramine, spiropyra/
The leuco type is preferred, and specific examples of these are shown below.

(a) Leuco compound of triphenylmethane dye represented by the following general formula: (wherein Rx, Ry and R2 are hydrogen, hydroxyl group, halogen, alkyl group, nitro group, amino group, dialkylamino group, monoalkyl group , allyl group.) Specific examples of the above leuco compounds are as follows.

3.3-bis(p-dimethylaminophenyl)-phthalide 3.3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide (also known as Gristal Violet Lacto/) 3.3-bis(p- (dimethylaminophenyl)-6-diethylaminophenyl 3.3-bis(p-dimethylaminophenyl)-6-chlorophthalide3.3-bis(p-dibutylaminophenyl)phthalide (b) Fluoran dye represented by the following general formula Leuco compound: In the formula, RX, R and R2 are the same as in the above (a).

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 f-'1 Fluoran dye Leuco compound: 3-diethylamino-6-methyl-7-chlorofluoran 3-pyrrolidino-6-methyl-7-anilinofluoran 2- (N-(3'-)lifluoromethylphenyl)amino)-6- Dinitylaminofluorane 2 (3,6-bis(diethylamino)-9-(o-
chloranilino)xatylbenzoic acid lactam) lactone compound represented by the following general formula: (Xa
)' unsubstituted phenyl group, cyanethyl group, or β-
Represents an ethyl halide group, or is a combination of R1 and R.CHz+4 p+CH+5 or +CHz+
? 0−+c represents H2+ 2 , 'R3 and R
4 represents hydrogen, a lower alkyl group, an alkyl group, an amino group, or a phenyl group, and either one of R3 and R4 is hydrogen, and p, xl, x, and X3 are hydrogen, a lower alkyl group, a group, or a lower alkoxyl group. , represents a halogen atom, a halogenated methyl group, a nitro group, an amino group, or a substituted amino group, Xa represents hydrogen, a halogen, a lower alkyl group or a lower alkoxyl group, and n is 0 or 1-4
represents an integer.

Specific examples of the above compounds are as follows.

3-(2'-hydroxy-4'-dimethylaminophenyl)-3-(z'-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-51-methylphenyl) phthalide.

In addition, binders for binding these substances to the support include polyvinyl alcohol, starch, starch derivatives, cellulose derivatives, water-soluble polymers such as polyacrylic acid copolymers, SBR latex, and styrene-acrylic acid esters. Aqueous emulsions such as .

In addition, inorganic and organic pigments such as calcium carbonate, clay, talc, zinc oxide, polystyrene pigments, and urea-formalin resin pigments are used to whiten and improve writing properties, and polyethylene wax and paraffin are used to improve head matching properties. It is also possible to add waxes such as wax, carnauba wax, montan wax, and higher fatty acid metal salts.

Generally known methods can be used to obtain the heat-sensitive recording sheet of the present invention using such materials. That is, color-forming substances, color-developing substances, binders, and the like. Other additives are added alone or mixed except for color-forming substances, and a colloidal substance such as polyvinyl alcohol, a surfactant, etc. are added, and the mixture is dispersed using a dispersing machine such as a ball mill, attritor, or sand mill, and then formulated. A heat-sensitive color forming layer coating solution is prepared according to the following procedure and coated on a support.

Next, Examples and Comparative Examples of the present invention will be shown.

Example 1 A mixture consisting of the following formulation was ground for one day in a magnetic ball mill to prepare a solid-liquid (2) liquid.

Solid-liquid 3-cyclohexylamino-6-methyl-7-anilinofluorane 150 Parts by weight 10 Polyvinyl alcohol aqueous solution 150 #Water 2
00 #(6) Liquid P-benzyl oxybenzoate 50
Part by weight P-oxybenzoic acid-P-chlorobenzyl
50 l calcium stearate
20 Calcium carbonate
100110% polyvinyl alcohol aqueous solution
100 parts by weight water
180 Next, liquid (2) and liquid (6) were mixed and stirred at a weight ratio of 1:5 to prepare a thermosensitive coloring layer liquid, and then
The dry coating amount is 51 on high-quality paper with a standard basis weight of 52 P/m.
A heat-sensitive recording sheet of the present invention was prepared by selecting a wire bar so as to have a ratio of #/TrL'', drying the coating, and calendering the coating so that the surface smoothness remained at Peck's smoothness level of 200 to 300 seconds.

Example 2 A heat-sensitive recording sheet of the present invention was prepared in exactly the same manner as in Example 1 except that the same weight of P-oxybenzoic acid-〇-methylbenzyl was used instead of P-chlorobenzyl P-oxybenzoate. .

Comparative Example 1 A comparative heat-sensitive recording sheet was prepared in exactly the same manner as in Example 1, except that methyl P-oxybenzoate (outside the present invention) was used instead of P-chlorobenzyl P-oxybenzoate. It was created.

Comparative Example 2 A heat-sensitive recording sheet for comparison was prepared using a formulation that did not contain P-chlorobenzyl P-oxybenzoate as in Solution B of Example 1.

The performances of the heat-sensitive recording sheet of the present invention and the comparative heat-sensitive recording sheet prepared as described above were compared, and the results are shown in Table 1.

Table 1 0: Rarely occurs Δ: Slightly occurs Energization time 2
．． 2m5ec 095W/1 dot), black flat printing was performed, and the recording density immediately after was shown. In addition, for powder blowing of the image, a sheet with solid black printing was filed and stored in an environment of 20° C. and 654 RH, and the state of the image surface was visually observed.

As is clear from Table 1, the heat-sensitive recording sheet of the present invention has no image powdering, has a high recording density, and has a white background, and is superior to the comparative heat-sensitive recording sheet.

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

Claims (1)

[Claims] (1) In a heat-sensitive recording sheet having a structure in which a heat-sensitive coloring layer is formed on a support, the color-developing layer is mainly composed of a generally colorless or light-colored Royce dye and a color-developing substance for the Royce dye, as the color-developing substance. , P− represented by the following general formula (1)
A heat-sensitive recording sheet characterized in that at least one oxybenzoic acid ester derivative and at least one P-oxybenzoic acid ester derivative represented by general formula (II) are used in combination. General formula (In (in the formula, %R1 is an alkyl group having 1 to 4 carbon atoms or a benzyl group)) General formula (In (in the formula, %R2 is a halogenated alkyl group having 1 to 4 carbon atoms,
(It is a halogenated benzyl group or an alkylated benzyl group having an alkyl group having 1 to 3 carbon atoms)