JPS61217285A - Thermal recording material - Google Patents

Abstract

PURPOSE:To provide excellent heat sensitivity and high color forming property and suppress fading and blushing of developed color images, by using a 2- hydroxy-6-naphthoic acid ester as a color developer. CONSTITUTION:A thermal color forming layer comprising a leuco dye and a color developer as main constituents is provided on a base. As the color developer is used a 2-hydroxy-6-naphthoic acid ester, advantagenously, an ester of general formula (I), wherein R5 is 1-8C alkyl, cyclohexyl, aryl or aralkyl, which may be haloor alkoxy-substituted. The 2-hydroxy-6-naphthoic acid ester is advantageously used in combination with a p-hydroxybenzoic acid ester and/or a bisphenol compound of general formula (II), wherein n is 1 or 2. Accordingly, a thermal recording material is provided which forms a color with high density and high sensitivity even where the energy supplied from a thermal head is low, and can record images which show little fading and blushing.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a heat-sensitive recording material that utilizes a color-forming reaction between a leuco dye and a color developer.

[Prior art]

Recently, various recording sheets have been researched and developed in the field of information recording and put into practical use in response to social demands such as diversification of information, increase in energy consumption, resource saving, and pollution-free society.Among them, thermal recording sheets ()'It is possible to record a colored image by simply heating it, eliminating the need for a complicated development process.
2) Recording can be done using a relatively simple and compact device, and the resulting recording sheets are easy to handle and maintenance costs are low; (3) Paper is often used as a support. In the second case, not only the cost of the support is low, but also the feel of the obtained recording sheet is similar to that of plain paper. It is widely used in the recorder field, low and high speed facsimile field, automatic ticket vending machine field, thermal copying field, etc.

The above-mentioned heat-sensitive recording material is produced by applying and drying a heat-sensitive coloring layer liquid containing a coloring component capable of causing 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 material thus obtained by heating it with a thermal pen or a thermal head.

Conventional examples of such heat-sensitive recording materials include, for example, Japanese Patent Publication No. 43-4160 or Japanese Patent Publication No. 45-140'39.
For example, such conventional heat-sensitive recording materials have low thermal responsiveness and cannot obtain sufficient color density during high-speed recording.

As a method for improving such drawbacks, for example, Japanese Patent Application Laid-Open No. 49-3
No. 4842 discloses acetamide, stearamide, m
-Nitrogen-containing compounds such as nitroaniline and dinitrile phthalate; JP-A-52-106746 describes acetoacetanilide; JP-A-53-11036 describes N,
N-diphenylamine derivatives, benzamide derivatives, carbazole derivatives, and in JP-A-53-3913.9, alkylated biphenyls and biphenylalkanes, and JP-A-56-144193.

The publication discloses a method of increasing speed and sensitivity by incorporating a P-oxybenzoic acid ester derivative, but among these methods, there is a method using a P-oxybenzoic acid ester derivative as a color developer. is said to be the most effective.

However, recently, the speed of thermal facsimile has become even faster.
As miniaturization is being considered, there is a growing demand for higher sensitivity of heat-sensitive recording sheets, and the above-mentioned methods for increasing sensitivity do not provide sufficiently satisfactory results.

Furthermore, the above-mentioned conventional color developers have the drawback that the recorded image may fade or the image area may become white (white powder is generated on the surface).

〔the purpose〕

31 The object of the present invention is to provide a highly sensitive thermosensitive recording material that improves the drawbacks of the prior art described above, that is, to provide a highly sensitive heat-sensitive recording material that develops color at high density even at low thermal head energy, and that prevents recorded images from fading. It is an object of the present invention to provide a heat-sensitive recording material that is less likely to cause whitening or whitening.

〔composition〕

According to the present invention, in a heat-sensitive recording material in which a heat-sensitive coloring layer containing a leuco dye and a color developer as main components is provided on a support,
A heat-sensitive recording material characterized in that 2-hydroxy-6-naphthoic acid ester is used as the color developer is provided.

In the present invention, 2-hydroxy-6-
Although naphthoic acid esters are used, those represented by the following general formula are advantageously used in the present invention.

(In the formula, R5 represents an alkyl group having 1 to 8 carbon atoms, a cyclohexyl group, an aryl group, or an aralkyl group, and these may further have a halogen or an alkoxyl group as a substituent.) Specific examples of the color developer include the following.

(1) 2-hydroxy-6-naphthoic acid methyl ester (2) 2-hydroxy-6-naphthoic acid ethyl ester (3) 2-hydroxy-6-naphthoic acid n-propyl ester (4) 2-hydroxy-6- Naphthoic acid 1so-propyl ester (5) 2-hydroxy-6-naphthoic acid n-butyl ester (6) 2-hydroxy-6-naphthoic acid 1so-butyl ester (7) 2-hydroxy-6-naphthoic acid 5ec-butyl ester Ester (8) 2-hydroxy-6-naphthoic acid cyclohexyl ester (9) 2-hydroxy-6-naphthoic acid noenyl ester (10) 2-hydroxy 6-naphthoic acid P-chlorophenyl ester (11,)' 2-hydroxy -6-naphthoic acid O-chlorophenyl ester (12) 2-hydroxy-6-naphthoic acid benzyl ester (13) 2-hydroxy-6-naphthoic acid m-methylbenzyl ester (14) 2-hydroxy-6-naphthoic acid P -Chlorobenzyl ester (15) 2-hydroxy-6-naphthoic acid phenethyl ester (16) 2-hydroxy-6-naphthoic acid 0-chlorobenzyl ester, etc.

The 2-hydroxy-6-naphthoic acid ester used as a color developer in the present invention is a conventionally known bisphenol A
It exhibits a higher sensitivity than that of the conventional method, and provides recorded images with less fading, whitening, and discoloration due to contact with oils, plasticizers, etc.

In the present invention, in order to increase the thermal sensitivity, thermofusible substances, particularly octahydroanthracene, P-benzylbiphenyl, acenaphthene, m-terphenyl, and 1-hydroxy-2-naphthoic acid, are used together with the color developer. When at least one selected from phenyl is used in combination, the effect of increasing sensitivity is greater than when higher fatty acid amides and the like are used together. These thermofusible substances are aromatic compounds with a melting point of 70 to 100°C, so they have a high ability to melt and dissolve the above color developer and leuco dye, and they have a high ability to melt and dissolve the color developer and leuco dye. It is thought that the sensitivity can be made higher than that of other methods.

The color developer used in the present invention is used in an amount of 1 to 10 times, preferably 2 to 5 times, the amount of the leuco dye on a weight basis, and the thermofusible substance is used in an amount of 1 to 10 times, preferably 2 to 5 times, the amount of the leuco dye on a weight basis. It is used in an amount of 0.5 to 10 times, preferably 1 to 5 times.

In addition, 2-hydroxy-6 used as a color developer in the present invention
-Naphthoic acid esters are advantageously used in combination with P-hydroxy-7=benzoic acid esters and/or bisphenol compounds of the general formula where n is an integer of 1 or 2. In this case, P-hydroxybenzoic acid esters include alkyl esters, cycloalkyl esters, aryl esters, aralkyl esters, etc., as in the case of the 2-hydroxy-6-naphthoic acid esters, and these alkyl, cycloalkyl esters, etc. Alkyl, aryl, and aralkyl groups can further have other substituents, such as halogen, alkoxyl groups, alkyl groups, and the like.

In the present invention, the P-hydroxybenzoic acid ester and bisphenol compound preferably used in combination with the 2-hydroxy-6-naphthoic acid ester are
Compared to hydroxy-6-naphthoic acid ester, it is slightly inferior in heat response and uniformity of colored images, but when eutectic with 2-hydroxy-6-naphthoic acid esters, it can prevent recrystallization of colored images and fading, Furthermore, it shows the effect of preventing discoloration due to contact with oils, plasticizers, etc. Therefore, by using a combination of the color developers described above, it is possible to obtain a heat-sensitive recording material that is highly sensitive and provides highly reliable colored images.

Here, the amount of the developer consisting of the above combination is 1 to 20 parts by weight, preferably 2 to 20 parts by weight, per 1 part by weight of the leuco dye.
If the amount used is 5 parts by weight, the coloring sensitivity will be poor, while if the amount is too large, the coloring density will be low. Also,
The P-hydroxybenzoic acid ester and/or bisphenol compound is used in a proportion of 0.01 to 10 parts by weight, preferably 0.1 to 1 part by weight, per 1 part by weight of 2-hydroxy-6-naphthoic acid ester. If the amount is less than 0.01 parts by weight, the reliability of the image deteriorates, while if it exceeds 20 parts by weight, the color development sensitivity deteriorates.

In the present invention, leuco dyes are used or a mixture of two or more types is used, and as such leuco dyes, those applied to this type of heat-sensitive material can be arbitrarily applied.
For example, leuco compounds of triphenylmethane-based, fluoran-based, phenothiazine-based, auramine-based, and spiropyran-based dyes are preferably used. Specific examples of such leuco dyes include those shown below.

3.3-bis(p-dimethylaminophenyl)-phthalide, 3.3-bis(p-dimethylaminophenyl)-6-dimethylami, nophthalide (also known as crystal violet lactone).

3.3-bis(P-dimethylaminophenyl)-6-diethylaminophenyl, 3.3-bis(P-dimethylaminophenyl)-6-chlorophthalide, 3.3-bis(p-dibutylaminophenyl)phthalide, 3 -cyclohexylamino-6-chlorofluorane, 3-dimethylamino-5,7-dimethylfluorane, 3
-diethylamino-7-chlorofluorane, 3-diethylamino-7-methylfluorane, 3-diethylamino-7,8-benzfluorane, 3-diethylamino-6
-Methyl-7-chlorofluorane, 3-(N-p-tolyl-N-ethylamino)-6-methyl-7-anilinofluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 2- (N-(3'-trifluoromethylphenyl)
amino)-6-dinithylaminofluorane, 2-(3,
6-bis(diethylamino)-9-(o-chloroanilino)xantylbenzoic acid lactam), 3-diethylamino-6-methyl-7-(m-trichloromethylanilino)fluoran, 3-diethylamino-7-(o-chloroanilino) ) fluoran, 3-dibutylamino-7-(o-chloroanilino)fluoran, 3-N-methyl-N-cyclohexylamino-6-methyl-7-anilinofluoran, =11- 3-diethylamino-6-methyl -7-anilinofluorane, 3-(N,N-diethylamino)-5-methyl-7-(
LN-dibenzylamino)fluoran, benzoylleucomethylene blue, 6'-chloro-8'-methoxy-benzoindolino-pyrylospirane, 6'-bromo-31-methoxy-benzoindolino-pyrylosvirane, 3-(2'-hydroxy) -4'-dimethylaminophenyl)-3-(2'-methoxy-51-chlorophenyl)phthalide, 3-(2'-hydroxy-4'-dimethylaminophenyl)-3-(2'-methoxy-5' -nitrophenyl)phthalide, 3-(2'-hydroxy-4'-diethylaminophenyl)-3-(2'-methoxy-51-methylphenyl)phthalide, 3-(2'-methoxy-4'-dimethylamino) phenyl)-3-(2'-hydroxy-4'-chloro-5'
-methylphenyl)phthalide, 3-morpholino-7-(N-propyl-trifluoromethylanilino)fluorane, 3-pyrrolidino-7-trifluoromethylanilinofluorane, 3-diethylamino-5-chloro-7-( N-benzyl-trifluoromethylanilino)fluoran, 3-pyrrolidino-7-(di-p-chlorophenyl)methylaminofluoran, 3-diethylamino-5-chloro-7-(α-phenylethylamino)fluoran, 3-(N-ethyl-p-)-luidino)-7-(α-phenylethylamino)fluoran, 3-diethylamino-7-(0-methoxycarbonylphenylamino)fluoran, 3-diethylamino-5-methyl-7 -(α-phenylethylamino)fluorane, 3-diethylamino-7-piperidinofluorane, 2-
Chloro-3-(N-methyltoluidino)-7-(p-n
-butylanilino)fluorane, 3-(N-benzyl-N-cyclohexylamino)-5
, 6-penzo 7-α-naphthylamino-4'-bromofluorane, 3-diethylamino-6-methyl-7-mesitidino 4
'=5'-benzofluorane etc.

In the present invention, as the main color developer, the above-mentioned ones are used, but in order to further improve the fading resistance and decolorization prevention property of the colored image, the following color developer may be added as appropriate. can do.

gallic acid, salicylic acid, 3-isopropylsalicylic acid,
3-cyclohexylsalicylic acid, 3,5-jer
t-Butylsalicylic acid, 3,5-di-α-methylbenzylsalicylic acid, 4,4'-isopropylidene diphenol, 4,4'-isopropylidene bis(2-chlorophenol), 4,4'-isopropylidene bis (2,6-
dibromophenol), 4,4'-isopropylidene bis(2,6-dichlorophenol), 4゜4'-isopropylidene bis(2-methylphenol), 4,4'-
Isopropylidene bis(2,6-dimethylphenol)
, 4,4'-isopropylidenebis(2-tert-butylphenol), 4,4'-5ec-butylidenediphenol, 4,4'-cyclohexylidenebisphenol, 4,4'-cyclohexylidenebis(2-tert-butylphenol) -methylphenol), 4-tert-butylphenol, 4
-Phenylphenol, 4-hydroxydiphenoxide, α-naphthol, β-naphthol, 3,5-xylenol, thymol, methyl-4-hydroxybenzoate, 4-hydroxyacetophenone, novolac type phenolic resin, 2,2'-thiobis( 4,6-dichlorophenol), catechol, resorcinol, hydroquinone, pyrogallol, phloroglycin, phloroglycin carboxylic acid, 4-tert-octylcatechol, 2,2'-
Methylenebis(4-chlorophenol), 2,2'-methylenebis(4-methyl-6-tert-butylphenol), 2゜2'-dihydroxydiphenyl, zinc salicylate, 1-hydroxy-2-naphthoic acid, 2-hydroxy- 6-naphthoic acid, zinc 2-hydroxy-6-naphthoic acid, 4-hydroxydiphenylsulfone, 4-hydroxy-4'-chlorodiphenylsulfone, bis(4-
hydroxyphenyl) sulfide, 2-hydroxy-P
-toluic acid, zinc 3,5-di-tert-butylsalicylate, tin 3,5-di-tert-butylsalicylate,
tartaric acid, oxalic acid, maleic acid, citric acid, succinic acid,
Stearic acid, 4-hydroxyphthalic acid, boric acid, etc.

In the present invention, in order to bind and support the leuco dye and color developer on the support, various commonly used binders can be used as appropriate, such as polyvinyl alcohol, starch and its derivatives, methoxycellulose, hydroxyl, etc. Cellulose derivatives such as ethyl cellulose, carboxymethyl cellulose, methyl cellulose, and ethyl cellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylic amide/acrylic ester copolymer, acryl amide/acrylic ester/methacrylic acid ternary copolymer, styrene/ Maleic anhydride copolymer alkali salt, isobutylene/maleic anhydride copolymer alkali salt,
In addition to water-soluble polymers such as polyacrylamide, sodium alginate, gelatin, and casein, polyvinyl acetate, polyurethane, polyvinyl chloride, polyvinylidene chloride, styrene/butadiene copolymer, polyacrylic acid, polyacrylic ester, and vinyl chloride. /vinyl acetate copolymer, styrene/acrylic acid ester copolymer, polybutyl methacrylate, ethylene/vinyl acetate copolymer, styrene/
Latex such as butadiene/acrylic copolymer can be used.

In addition, in the present invention, in addition to the leuco dye and color developer, if necessary, auxiliary additive components commonly used in this type of heat-sensitive recording material, such as fillers, surfactants, thermofusible substances ( or lubricant) etc. can be used in combination. In this case, fillers include, for example, calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, clay, talc, and surface-treated inorganic fine powders such as calcium carbonate and silica. Others, urea-
Organic fine powders such as formalin resin, styrene/methacrylic acid copolymer, and polystyrene resin can be mentioned, and examples of thermofusible substances include higher fatty acids or their esters and amides (including their methylolated products). In addition to metal salts, various waxes, dimethyl terephthalate, condensates of aromatic carboxylic acids and amines, phenyl benzoate, higher linear glycols, dialkyl 3,4-epoxy-hexahydrophthalate, higher ketones. ,
Examples include other thermofusible organic compounds having a melting point of about 50 to 200°C. Furthermore, if necessary, an undercoat layer made of a filler or a water-soluble binder can be provided between the support and the thermosensitive coloring layer.

Generally known methods can be used to obtain the heat-sensitive recording material of the present invention. That is, a leuco dye, a color developer, a binder, and other additives may be used alone or in a mixture other than the leuco dye, and a protective colloid substance such as polyvinyl alcohol, a surfactant, etc. may be added to the ball mill, attritor, etc.
After dispersing with a dispersing machine such as a sand mill, a heat-sensitive coloring layer coating solution is prepared according to the recipe, coated on a support such as paper, synthetic paper, film, etc., dried, and then calendered to produce the heat-sensitive recording of the present invention. Materials are obtained.

〔effect〕

The heat-sensitive recording material of the present invention has the above-mentioned structure, has excellent thermal sensitivity, exhibits high color development, and prevents fading and whitening of colored images.
It also has excellent image reliability with extremely little discoloration when it comes into contact with oil, plasticizers, etc.

〔Example〕

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 (Liquid A(1)) 3-(N-methyl-N-cyclohexyl)amino-7-
Aniritsu fluoran 300 parts 10% polyvinyl alcohol aqueous solution 300 parts water
400 parts [Liquid B (1)] Color developer shown in Table 1 IOO parts Calcium carbonate 100 parts Sensitizer shown in Table 1 100 parts Polycarboxylic acid type surfactant 5 parts 10% polyvinyl alcohol aqueous solution 300 parts Water
A (1) liquid and a B (1) liquid were prepared by grinding and dispersing each of the mixtures having the following compositions using a sand glider for 2 to 4 hours.

Next, liquid A(1) and liquid B(1) are mixed in a weight ratio of A:B=1.
: 9 to prepare a heat-sensitive coating solution.

Next, this heat-sensitive coating liquid was applied and dried on high-quality paper with a basis weight of 52 g/ni' at a coating amount of 5 g/% after drying, and the resulting coated paper was coated with a Beck smoothness of 700-1, 200
A heat-sensitive recording material was prepared by calendering so that the temperature became secltF.

The above heat-sensitive recording materials were tested for dynamic color development sensitivity, image fading resistance, and whitening.

The results are shown in Table-1. The test method was performed as follows.

(1) Dynamic color development sensitivity: Heat-sensitive printing experimental equipment manufactured by Matsushita Electronics Co., Ltd. with a thin film head, Herad power applied 0.4511/dot, ■ Line recording time 20 m
5/ Q, scanning line density 8 x 3.85 dots/mm, pulse width O, S, 1.2.1.6.2.0 m5
Print with EC and measure the print density with Macbeth Densitometer RD-5.
Measured at 14.

(2) Image fading rate...For the samples whose dynamic color development sensitivity was measured in (1), those with a print density of 1.0 to 1.2 (this is Do) were left at room temperature for 15 days. The subsequent density was measured and designated as D), and the image fading rate was determined in accordance with the following.

(3) Image whitening... Perform the same test as (2),
Judgment was made by visual inspection as follows.

○: Almost no white powder generated Δ: White powder generated, but no practical problem An experiment was conducted in the same manner as in 2), and the following judgments were made.

O: Image fading rate less than 30% △: Image fading rate 30-50% ×: Colorimetric fading rate 50% or more Example 2 [Liquid A (2)] 3-N-Methyl-N-cyclohexylamino-6- Methyl-7-anilinofluorane 20 parts Itaconic acid-modified polyvinyl alcohol alkali salt 10% aqueous solution 20 parts Water

60 parts (Liquid B(2)) Color developer shown in Table 2 (1) 15 parts Color developer shown in Table 2 (■) 5 parts Calcium carbonate 20 parts Itaconic acid modified polyvinyl alcohol alkali salt 10% aqueous solution 20 Department water
4
0 parts Each of the mixtures with the above compositions was dispersed in a ball mill for 100 hours, 20 parts of liquid A (2) and 80 parts of liquid 8 (2) were mixed and stirred, and this heat-sensitive coating liquid was applied to a piece of high-quality paper with a basis weight of 50 g/if. A heat-sensitive recording material is obtained by coating and drying liquid A(2) so that the weight after drying is 0.5 g/rrr.

Next, the heat-sensitive recording material obtained as described above was tested for dynamic color development sensitivity, image fading rate, image whitening, and oil resistance in the same manner as in Example 1, and the results are shown in Table 2.
Shown below.

In Table 1, the symbols shown next to the color developer mean the following.

Ni-A: Ni-b: 11rWJ08G1-217285 (9) Example 3 [Liquid A (3)] 3-N-Methyl-N-cyclohexylamino-6-methyl-fluorane 20 parts Itaconic acid-modified polyvinyl Alcohol alkali salt 10% aqueous solution 20 parts water

60 parts (B(3) solution) Color developer shown in Table-3 [1] 15 parts Color developer shown in Table-3 [■] 5 parts Calcium carbonate 20 parts Itaconic acid modified polyvinyl alcohol alkali salt 10% aqueous solution 20 parts water

40 parts of each mixture of the above composition was dispersed in a ball mill for 100 hours, 20 parts of liquid A (3) and 80 parts of liquid B (3) were mixed and stirred, and this heat-sensitive coating liquid was coated on high-quality paper with a basis weight of 50 g/rd. A heat-sensitive recording material was obtained by coating and drying the liquid A(3) so that the weight after drying was 0.5 B/rd.

Next, the heat-sensitive recording material obtained as described above was tested for dynamic color development sensitivity, image fading rate, image whitening, and oil resistance in the same manner as in Example 17, and the results are shown in Table 3.
Shown below.

JP-A-6L-217285 (11) 1 “ domain mouth Weir two legs Kube Soba -) i-tube tin #C

Claims (4)

[Claims] (1) A heat-sensitive recording material in which a heat-sensitive color forming layer containing a leuco dye and a color developer as main components is provided on a support, characterized in that 2-hydroxy-6-naphthoic acid ester is used as the color developer. A heat-sensitive recording material. (2) Octahydroanthracene, P
- The heat-sensitive recording material according to claim 1, which contains at least one thermofusible substance selected from benzylbiphenyl, acenaphthene, m-terphenyl, and phenyl 1-hydroxy-2-naphthoate. (3) The heat-sensitive recording material according to claim 1, which uses a combination of 2-hydroxy-6-naphthoic acid ester and P-hydroxybenzoic acid ester as the color developer. (4) The color developer includes 2-hydroxy-6-naphthoic acid ester and bisphenol represented by the general formula ▲ mathematical formula, chemical formula, table, etc. ▼ (in the formula, n is an integer of 1 or 2) A heat-sensitive recording material according to claim 1, which is used in combination with a compound.