JPS6377779A - Thermal sensitive recording medium - Google Patents

Abstract

PURPOSE:To enhance the retention stability of a recording image by providing a thermal sensitive recording layer which contains a leuco dye represented by a specific general formula and a sensitizer represented by the specific general formula on a support. CONSTITUTION:A leuco dye represented by a formula I and a sensitizer represented by a formula II are mixed to prepare a thermal sensitive coloring layer forming coating solution. A support, such as sheet, synthetic sheet, or resin film is coated with the solution to form a thermal sensitive recording layer, and a thermal sensitive recording medium is manufactured. A material for bonding the compounds of the formulae I, II onto the support can use aqueous soluble non nonaqueous soluble resin binder, but preferably use aqueous soluble resin, such as casein, gelatin, polyvinyl alcohol, starch, isobutylene-maleic an hybride resin, etc.

Description

Detailed Description of the Invention <Industrial Application Field> The present invention relates to a heat-sensitive recording medium with improved storage stability, and more specifically, to a heat-sensitive recording medium with improved storage stability, and more specifically, to prevent the adhesion of chemicals such as oil and plasticizers that occur during storage of thermally recorded images. The present invention relates to a heat-sensitive recording material that has improved discoloration due to fingerprints, fingerprints, etc.

<Prior art> In general, a heat-sensitive recording material made by coating a support with a colorless or light-colored leuco dye and a color developer that develops the color when heated is disclosed in Japanese Patent Publication No. 14035/1983, etc. ,
A thermal printer with a built-in thermal head is used to record on this thermal recording medium, but compared to other recording methods, this thermal recording method has the following advantages: (1) Printers for computer output, facsimiles, calculators, etc. have the following characteristics: no noise, (2) no need for developing and fixing, (3) maintenance-free, and (4) relatively inexpensive and compact equipment. , measurement recorder, automatic ticket vending machine,
Widely used in fields such as thermal recording label printers.

However, heat-sensitive recording materials using this type of heat-sensitive recording bonding have problems in storage stability of images.

For example, contact with polyvinyl chloride film, plasticizer-containing materials such as plastic erasers, adhesion of oils such as cooking oil and industrial oil, contact with adhesives such as celco tape, stick glue, etc. has the disadvantage that the image easily fades due to the adhesion of fingerprints and the like. Therefore, it is inconvenient to use it in applications that require long-term image stability or where there is a possibility of contact with the above-mentioned chemicals.

Therefore, various attempts have been made to improve the storage stability of the images and to use this type of heat-sensitive recording in a wider range of applications.

For example, in JP-A-5'7-188392, a heat-sensitive coloring layer-
It has been proposed that a protective layer be provided on 1- to prevent penetration of chemicals such as plasticizers and oils. However, since the protective layer impedes heat conduction, recording sensitivity is poor (and, furthermore, a coating process for the protective layer is required, resulting in high costs).

Further, discoloration occurs due to penetration of chemicals through the protective layer's vinyl poles and the cross section of the recording medium.

Attempts have also been made to improve the storage stability using color developers and additives. For example, as a color developer, sulpol diphenol compound is used (Japanese Patent Application Laid-Open No. 57-187
293), using a bisphenol sulfide compound (JP-A-57-8187.57-39987.57-4)
1996>, including 4-hydroxyzalitylanilide (Japanese Unexamined Patent Publication No. 58-49294), and many other proposals have been made. In addition, the additives include sulfonic acid derivatives (JP-A-59-73990) and 2-cho-Dokubenzoic acid metal salt derivatives (JP-A-6O-61289).
Although many proposals have been made, the current situation is that a thermosensitive recording material with satisfactory storage stability has not yet been obtained.

<Problems to be Solved by the Invention> In view of the above problems, the present inventor investigated the cause of discoloration of recorded images due to chemicals such as plasticizers and oils, and discovered that the cause melts when heated and develops color. It was discovered that the solubility of the reaction product of the leuco dye and the color developer in chemicals such as plasticizers and oils. That is, the lower the solubility of the reaction product between the leuco dye and the color developer in chemicals, the better the image stability. This solubility cannot be sufficiently improved just by selecting materials for color developers and additives as in the conventional technology (this suggests that it is also necessary to consider leuco dyes; This means that the storage stability of images can only be improved by combining them with colorants.

Based on the above study results, the present inventors have investigated various combinations of leuco dyes and color developers, which have very low solubility in plasticizers and oils, and have found that they can produce thermal recording materials with excellent storage stability. has been developed.

<Means for Solving the Problems> The present invention provides a heat-sensitive recording material in which a heat-sensitive color-forming layer mainly composed of a leuco dye and a color developer that causes the leuco dye to develop color when heated is provided on a support. The leuco-4-dye is a compound represented by the following formula [1], the color developer is a compound represented by the following formula [2], and the present invention provides a heat-sensitive recording material characterized by a leuco-4-dye. .

[1] Formula [2] Formula It is preferable to use the above-mentioned leuco dye of formula [1] according to the present invention, but other colorless or light-colored leuco dyes may be used as long as they do not impair storage properties. Can also be used in combination with Examples of specific compounds of leuco dyes that can be used in combination include crystal violet 1-heractone, 3-diJ
, delamino-7-chloroL1 fluorane, 3-diethylamino-6-methyl-roof-chlorofluorane, 3-cyclohexylamino-6-chlorofluorane, 3-diethylamino-7-dibenzylaminofluorane, 3 -pyrrolidino-6-methyl-7-anilinofluorane, 3-
piperidino-6-methyl-7-anilinofluorane, 3
-cyclohexylmethylamino-6-methyl-7-anilinofluorane, 3-ethylisoamylamino-6-methyl-7-anilinofluorane, 3-diethylamino-
Examples include 7-(o-chloroanilino)fluoran and 3-dibdelamino-7-(0-chloroanilino)fluoran.

The ratio of the leuco dye that can be used in combination is 0 to 60% by weight, preferably 40% by weight or less, based on the leuco dye of formula [1] above.

Although it is preferable to use the color developer of formula [2] alone in the present invention, it may be used in combination with one or more of the color developers described below as long as storage stability is not impaired. Color developers used in combination include α-naphthol, β
-Naph I-ru, 4-t-butylphenol, 4-t
-octylphenol, 4-phenylphenol, 2,
2-bis(p-hydroxyphenyl)propane, 2.2
-(p-hydroxyphenyl)butane, 4,4'-cyclohexylidene diphenol, 2,2-bis(2,5-
dibromo-4-hydroxyphenyl)propane, 4.4
'-Isopropylidene bis(2-t-butylphenol), 2,2'-methylenebis(4-chlorophenol)
, 4,4'-sulfonyldiphenol, 4,4°-thiobisphenol, benzoic acid, salicylic acid, tartaric acid, gallic acid and other derivatives.

In the present invention, a material for binding the leuco dye of formula [1] and the color developer of formula [2] to a support, such as paper, synthetic paper, resin film, or a composite thereof. Water-soluble or water-insoluble resin binders can be used, but water-soluble resins are preferred, such as casein, gelatin, polyvinyl alcohol, polyvinylpyrrolidone, starch, modified starch, isobutylene-maleic anhydride, etc. 8 = Resin, cyisobutylene-maleic anhydride resin, styrene-maleic anhydride resin, polyacrylamide, modified polyacrylamide, carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose, furthermore, vinyl acetate, acrylic ester, vinyl chloride-vinyl acetate copolymer, Emulsions such as SBR and %NBR, latex, etc. can be used alone or in combination. Moreover, it is also possible to add a waterproofing agent if necessary.

In addition, the heat-sensitive coloring layer in the present invention includes inorganic and organic pigments as conventional fillers, such as heavy and light calcium carbonate, aluminum hydroxide, titanium oxide, zinc oxide,
The clarity of the colored image can be improved by adding barium sulfate, talc, clay, satin white, kaolinite, polyolefin particles, polystyrene particles, urea-formalin resin particles, etc.

Furthermore, various heat-fusible substances can be added to the heat-sensitive color forming layer as used in the present invention, if necessary, in order to improve the recording sensitivity. Thermofusible substances include organic compounds with appropriate melting points, such as higher fatty acid amides such as stearic acid amide, animal waxes such as beeswax and shellfish wax, vegetable waxes such as carnauba wax, and montan wax. Waxes such as mineral waxes such as paraffin waxes and microcrystalline waxes, higher fatty acids, higher fatty acid esters, aromatic carboxylic acid esters such as dimethyl terephthalate and diphenyl phthalate, alkylnaphthalene derivatives, alkyldiphenyl derivatives, and alkylterphenyl derivatives. etc. are used.

In addition, lubricants such as zinc stearate and calcium stearate, various surfactants, antifoaming agents, and the like are added as necessary.

The heat-sensitive recording material of the present invention basically has a high degree of image storage stability without requiring a protective layer, which has heretofore been provided on a heat-sensitive coloring layer to prevent penetration of chemicals. However, providing the heat-sensitive recording material of the present invention with a protective layer having the above-mentioned function is clearly an effective means for further improving storage stability.

The protective layer is mainly formed of a resin having excellent film-forming properties and excellent chestnut resistance. The resin for the protective layer is preferably a water-soluble polymer, such as polyvinyl alcohol, modified polyvinyl alcohol, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, starch and its derivatives, casein, sodium alkinate, polyvinylpyrrolidone, polyacrylamide, modified Resins such as polyacrylamide are used. In addition, in order to increase the water resistance of the protective layer, glyoxal is added as a water resistance agent.
Chrome bright pan, melamine resin, melamine formaldehyde resin, polyamide resin, polyamide-epichlorohydrin resin, etc. are added, and pigments, waxes, etc. are added for matching with the heat-sensitive recording head.

<Example> The present invention will be explained in detail below with reference to Examples.

Example: Mixtures with the following compositions were each ground in a ball mill for one day.
[Δ1 to [C] solutions were prepared by dispersing.

[Liquid A1 [1] Leuco dye represented by the formula 25 parts 5z Hydroxyethyl cell "1-su aqueous solution 50 parts water
25 parts [B] Liquid [2] Color developer represented by formula 20 parts 5z hydroxyethyl cellulose aqueous solution 50 parts Stearamide 10 parts Water
20 parts [C] Liquid light calcium carbonate 40 parts 1 Old polyvinyl alcohol aqueous solution 40 parts Water
Using 20 parts of liquids [A] to [C] obtained as above, a heat-sensitive coloring layer paint having the following formulation was prepared, and a dry coating amount of 5 to 6 g/n was applied to high-quality paper weighing 45 g/J. ? It was coated and dried.

Furthermore, the heat-sensitive recording material of the present invention was prepared by calendering so that the smoothness of the heat-sensitive coloring layer was 400 to 600 seconds.

-12 = Thermosensitive coloring layer paint [Al liquid 30 parts [B]
Liquid 100 parts [C] Liquid
100 parts 10 Nepolyvinyl alcohol aqueous solution 100 parts Comparative Example 1 A thermosensitive recording material was prepared in the same manner as in the example except that the following Dl liquid was used instead of the Al liquid in the example.

[D] Liquid 3-cyclohexylmethylamino-6-methyl-7-anilite fluorane 25 parts 5-hydroxyethylcellulose aqueous solution 50 parts water
25 parts Comparative Example 2 A thermosensitive recording material was produced in the same manner as in the example except that the following El solution was used instead of the liquid [B] in the example.

[E] Solution 2.2 His(p-hydroxyphenyl)propane 20 parts 5z Hydroxyethyl cellulose aqueous solution 50 parts Stearamide 10 parts Water
20 parts Comparative Example 3 A thermosensitive recording material was produced in the same manner as in the example except that the following liquid [F] was used instead of the liquid [B] in the example.

[F] Liquid 4.4”-sulfonyldiphenol 20 parts 5
Zero hydroxyethyl cellulose aqueous solution 50 parts Stearamide 10 parts Water
20 parts Comparative Example 4 A thermosensitive recording material was prepared in the same manner as in the example except that one liquid was used instead of the Al liquid and the El liquid was used instead of the IBI liquid.

The heat-sensitive recording materials of Examples and Comparative Examples obtained as described above were tested at a temperature of 150°C using a thermal gradient tester (manufactured by Toyo Seiki Co., Ltd.).
A heat block was contacted for 3 seconds at a pressure of i-kg/cJ to develop color and form a printed part.

The following storage stability test was conducted for the Examples and Comparative Examples to evaluate storage stability.

(a) Oil resistance test The thermosensitive recording material was immersed in cottonseed oil for 10 minutes and then taken out.
Leave it in an atmosphere of 40°C for 24 hours. After standing, the density of the printed area was measured using a Macbeth densitometer (RD-914).
Compare with the concentration before the test.

(b) Plasticizer resistance test An eraser manufactured by Plusdeck (MONOFF-01) (manufactured by Mbo Co., Ltd.) was applied to the printed area of a heat-sensitive recording material at a rate of 500 g/cn? Contact them at a pressure of Measure the density of the printed area after standing and compare it with the density before the test.

(C) Apply cellophane tape (Scottish Mending Tape manufactured by Sumitomo 3M Co., Ltd.) to the printed area of the adhesive-resistant thermosensitive recording material, and measure the density before the test. Leave it for one month in an atmosphere at 40°C, and compare the concentration after leaving it with the concentration before the test.

The results of each test are listed in Table-1.

Table 1 <Effects of the Invention> As is clear from Table 1, a thermosensitive recording layer provided with a thermosensitive coloring layer containing a leuco dye of formula [1] and a color developer of formula [2] according to the present invention. It has been confirmed that the image has remarkable storage stability, and that it has excellent durability with no practical problems even in applications where it has been difficult to use due to lack of storage stability. Ta.

Claims (1)

[Scope of Claims] A heat-sensitive recording material provided with a heat-sensitive coloring layer mainly composed of a leuco dye and a color developer that causes the leuco dye to develop color when heated on a support, wherein the leuco dye is represented by the following formula [1]. A heat-sensitive recording material, wherein the color developer is a compound represented by the following formula [2]. [1] Formula ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ [2] Formula ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼