JPH0115395B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat-sensitive recording sheet which has extremely excellent color development sensitivity. Thermal recording sheets print characters and characters using thermal energy.
It allows images such as figures to appear on a recording sheet, and has recently come to be used in fields such as various printer recorders and facsimile machines. There are various heat-sensitive recording methods, but from the viewpoint of image clarity, resolution, image tone, etc., we use a color-forming lactone compound, such as crystal violet lactone, which is a dye precursor, and an acidic substance that develops the color. The method used is the mainstay. In this method, bisphenol A is used as a color developer, which is solid at room temperature, but when heated, it melts into a liquid and acts as an acid component.
Phenol compounds such as At this time, the heat-sensitive material is required to have high whiteness and to be resistant to decrease in whiteness even during storage. Usually, in order to obtain vivid color development, it is necessary to maintain the temperature at around 140 to 150°C for a certain period of time. Therefore, various approaches have been widely researched and reported in order to develop colors faster and more easily and vividly. For example, JP-A-53-5636
Please refer to the following published patent publications: JP-A-53-11036, JP-A-53-26139, and JP-A-53-39139. However, the measures described in these publications are
Although the color development sensitivity was improved, it was still not satisfactory. In view of this situation, the inventors of the present invention have conducted various studies and found a compound that has a significantly superior improvement effect compared to conventional color development sensitivity improvers, and has accomplished the present invention. That is, the present invention provides a heat-sensitive recording sheet that is heat-sensitively colored with a color-forming lactone compound and an acidic substance, in which one or more esters consisting of o-hydroxynaphthoic acid methyl ester, ethyl ester, and phenyl ester are used as a color development sensitivity improver. Provided is a heat-sensitive sheet characterized by containing: As the color development sensitivity improver of the present invention as described above,
Examples include 1-hydroxy-2-naphthoic acid phenyl ester, 2-hydroxy-3-naphthoic acid methyl ester, 2-hydroxy-3-naphthoic acid ethyl ester, 2-hydroxy-3-naphthoic acid phenyl ester, etc. Can be done. The heat-sensitive recording sheet of the present invention has excellent storage stability and, moreover, extremely excellent color development sensitivity. Although the reason for this is not clear, it can be inferred as follows. The specific esters used as coloring sensitivity improvers in the present invention are a type of carboxylic acid ester, and do not have any effect at room temperature, but acidic substances such as bisphenol A that are melted and liquefied by heating can be used as crystal violet lactone. It is thought that the above-mentioned esters are hydrolyzed more quickly than they are reacted, and the resulting carboxylic acid then promotes the ring opening of crystal violet lactone, thereby significantly accelerating color development. This is because sulfonic acid esters are extremely stable against acidic hydrolysis and therefore do not act as a color development sensitivity improver at all. Also,
Benzoic acid alkyl ester, terephthalic acid ethyl ester, phosphoric acid phenyl ester, coumarin, etc. are active against acidic hydrolysis and produce carboxylic acids and phosphoric acids that are more acidic than phenols, so they have the effect of improving color development sensitivity. Although it has some properties, it acts slightly even at room temperature and lacks the ability to maintain the whiteness of the sheet during storage and before and after use. Furthermore, since the coloring sensitivity improver used in the present invention has an ultraviolet absorbing effect, it is possible to improve the ability of the sheet to maintain whiteness during storage and before and after use, and also to improve the light resistance of the coloring dye. Now, the color-forming lactone compound in the present invention is, for example, 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-aminophthalide, 3,3-bis(p-dimethylaminophenyl)-6-nitrophthalide, 3,3-bis(p-dimethylaminophenyl) phthalide),
3,3-bis(p-dimethylaminophenyl)-
Triphenylmethanephthalides such as 4,5,6,7-tetrachlorophthalide, 3-dimethylamino-7-methylfluoran, 3-diethylamino-
7-chlorofuran, 3-diethylamino-6-chloro-7-methylfluoran, 3-diethylamino-7-anilinofluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-
Piperidino-6-methyl-7-anilinofluorane, 3-(N-ethyl-p-toluidino)-7-
Fluoranphthalides such as (N-methylanilino)fluoran, lactams such as rhodamine B lactam, 3-methylspirodinaphthobilane, 3-
Examples include spiropyrans such as ethylspirodinaphthopyran and 3-benzylspironaphthopyran. Of course, these compounds must be colorless or light-colored and develop color when reacting with acidic substances. In addition, acidic substances are solid at room temperature and are
When heated to about 180°C, it melts and liquefies and hydrolyzes the lactone ring of the color-forming lactone compound to develop color. Examples include 4-phenylphenol, 4-hydroxyacetophenone, 2,2'-dihydroxydiphenyl, 2,2'-
methylenebis(4-chlorophenol), 2,
2'-methylenebis(4-methyl-6-t-butylphenol), 4,4'-isopropylidenediphenol (also known as bisphenol A), 4,4'-isopropylidenebis(2-chlorophenol), 4,
4'-isopropylidene bis(2-methylphenol), 4,4'-ethylenebis(2-methylphenol), 4,4'-thiobis(6-t-butyl-3
-methylphenol), 1,1-bis(4-hydroxyphenyl)-cyclohexane, 2,2'-bis(4-hydroxyphenyl)-n-heptane,
4,4'-cyclohexylidene bis(2-isopropylphenol), 4,4'-sulfonylbisphenol, salicylic acid anilide, novolac type phenolic resin, benzoic acid, pt-butylbenzoic acid, o- or p-chloro benzoic acid, dichlorobenzoic acid, trichlorobenzoic acid, m- or p-hydroxybenzoic acid, o-, m- or p-toluic acid,
Phthalic acid, isophthalic acid, terephthalic acid, gallic acid, trimellitic acid, salicylic acid, 3- or 4-
Examples include ethylsalicylic acid, 3- or 5-phenylsalicylic acid, 3-, 4-, 5- or 6-hydroxysalicylic acid, α- or β-naphthoic acid, and the like. These acidic substances are chromogenic lactone compounds100
Usually 200 parts by weight (hereinafter simply referred to as parts)
~3000 parts, preferably 500-2500 parts are used. The color development sensitivity improver is usually used in an amount of 0.5 to 200 parts, preferably 1 to 50 parts, per 100 parts of the acidic substance. The color-forming lactone compound, the acidic substance, and the color-forming sensitivity improver are all used in the form of fine particles, preferably fine particles having a particle diameter of several microns or less. A variety of generally known methods can be used to produce a heat-sensitive recording sheet, but usually a coating solution is prepared by dispersing a color-forming lactone compound, an acidic substance, and a color-forming sensitivity improver in water, and then this is applied. Method for applying to the sheet substrate Prepare a coating liquid in which a color-forming lactone and an acidic substance are separately dispersed in water, at least one of which contains a coloring sensitivity improver, and apply these coating liquids to the sheet substrate. A method such as layered coating can be adopted. Of course, the above coating liquid may contain binders such as polyvinyl alcohol,
Methylcellulose, hydroxyethylcellulose, carboxymethylcellulose, starches,
Add an aqueous binder such as a styrene-maleic acid copolymer. In addition, in order to improve performance, the coating liquid may contain ultraviolet absorbers such as benzophenone and triazole, fillers such as kaolin, talc, and calcium carbonate, lubricants such as polyethylene wax and paraffin wax, and waterproofing agents. A curing agent and various other chemicals can be added. Furthermore, various dispersants for dispersing various drugs in water can be added to the coating liquid. The coating solution is applied to the sheet substrate so that the color-forming lactone compound contained therein is generally 0.1 to 0.6 g per 1 m ² of the sheet substrate, and then heated at room temperature to 50°C.
The heat-sensitive recording sheet of the present invention can be obtained by drying the sheet at a temperature of about 100 ml. Paper is generally used as the sheet base material, but synthetic resin sheets, nonwoven fabric sheets, etc. can also be used as appropriate. EXAMPLES Next, the present invention will be specifically explained with reference to Examples, but the present invention is not limited thereto in any way. In the examples, parts mean parts by weight unless otherwise specified. Example 1 A ¹ part 3-diethylamino-6-methyl-7-anilinofluorane 10 parts 5% hydroxyethyl cellulose aqueous solution 10 parts Water 10 parts B Liquid bisphenol A 10 parts 5% hydroxyethyl cellulose aqueous solution 10 parts Water 10 parts C Liquid 2-hydroxy-3-naphthoic acid phenyl ester 10 parts 5% hydroxyethyl cellulose aqueous liquid 10 parts Water 10 parts A ¹ , B and C were each placed in separate ball mills.
They were pulverized and dispersed to obtain respective coating solution stock solutions. Next, they were mixed in the following proportions to obtain a heat-sensitive coating liquid. A: ¹ part 0.5 parts B: 2.5 parts C: 0.5 parts 5% hydroxyethyl cellulose aqueous solution
5.3 parts This heat-sensitive coating liquid was applied onto a base paper having a basis weight of 50 g/m ² so that the coated amount after drying was 3 g/m ² , and dried to obtain a heat-sensitive recording paper. In addition, a heat-sensitive coating liquid that does not contain a coloring sensitivity improver is used: A ¹ part 0.5 parts B part 2.5 parts 5% hydroxyethyl cellulose aqueous solution
5.3 parts of the mixture and similarly coated on a base paper with a basis weight of 50 g/m ² to a coating weight of 3 g/m ² after drying. I got the recording paper. Clear records could be obtained on both of these two types of thermal recording paper and commercially available thermal recording paper using Panafax 7000 (facsimile manufactured by Matsushita Electric Transmission Co., Ltd.). Next, set the voltage applied to the thermal head of the facsimile to the specified voltage of 14.7V.
When I lowered it to 10.0V and recorded it,
The recordings on the commercially available thermal recording paper and the thermal recording paper not containing the coloring sensitivity improver were unclear, but the recordings on the thermal recording paper containing the coloring sensitivity improving agent were clear. Example 2 A ^Two -part crystal violet lactone 10 parts 5% hydroxyethyl cellulose aqueous solution
10 parts water 10 parts A ² liquids were placed in a ball mill and pulverized and dispersed to obtain a paint stock solution. Next, A ² parts 0.5 parts B part 2.5 parts 5% hydroxyethyl cellulose aqueous solution
A ₂ parts 0.5 parts B 2.5 parts 5% hydroxyethylcellulose aqueous solution in the same manner as described in Example 1 in the proportion of 5.3 parts
A heat-sensitive coating liquid was prepared in a proportion of 5.3 parts, and the thickness after drying was 0.04 mm on a polyester film with a thickness of 0.2 mm.
mm and dried to obtain a heat-sensitive recording sheet containing no color development sensitivity improver (standard) from each heat-sensitive coating liquid. Next, each of the various coloring sensitivity improvers shown in Table 2 was mixed with 10 parts of a 5% hydroxyethyl cellulose aqueous solution.
A coating liquid stock solution containing a color development sensitivity improver was prepared by pulverizing and dispersing the mixture in a ball mill in a ratio of 10 parts water to 10 parts. Next, A ¹ part 0.5 parts B part 2.5 parts Coating solution stock solution containing color development sensitivity improver 0.5 parts 5% hydroxyethyl cellulose aqueous solution
Heat-sensitive coating liquid consisting of 5.3 parts, and A ² parts 0.5 parts B liquid 2.5 parts Coating liquid stock solution containing color development sensitivity improver 0.5 parts 5% hydroxyethyl cellulose aqueous solution
A heat-sensitive coating liquid consisting of 5.3 parts was prepared, applied to a polyester film in the same manner as above, and dried to produce a heat-sensitive recording sheet containing each color development sensitivity improver. The standard sheet that does not contain the color sensitivity improver and the sheet that contains the color sensitivity improver obtained in this way are
Color was developed by heating at 80°C for 5 seconds. As a result, the standard sheet showed almost no color development, but the sheet containing the color development sensitivity improver developed color. In order to compare the degree of color development, each sheet was heated at 80°C for 5 seconds to develop color, and a standard sheet containing no sensitivity enhancer was heated sufficiently to develop color. The color difference ΔE was determined using an Applied Color Systems System 500 spectrophotometer. The results are shown in Table 2. Note that the smaller the number, the better the sensitivity. As is clear from Table 2, it can be seen that the sensitivity of the heat-sensitive recording sheet containing the novel sensitivity improver of the present invention is significantly improved. Moreover, the heat-sensitive recording sheet of the present invention has a high degree of whiteness, and there is no decrease in whiteness during storage. 【table】

Claims (1)

[Claims] 1. In a heat-sensitive recording sheet that is heat-sensitively colored with a color-forming lactone compound and an acidic substance, one or more types of esters consisting of methyl ester, ethyl ester, and phenyl ester of O-hydroxynaphthoic acid are contained as a color development sensitivity improver. A heat-sensitive recording sheet characterized by: