JPH06320872A - Thermal recording material - Google Patents

Abstract

PURPOSE:To obtain a thermal recording material imparting an image excellent in heat stability and recording quality by providing a thermal recording layer containing a dye precursor, an electron acceptive compd. and a specific phenolic compd. on a support. CONSTITUTION:A dye precursor, an electron acceptive compd. allowing the dye precursor to develop a color and a phenolic compd. represented by formula (wherein R is an alkyl group which may have a substituent, an alkenyl group or aralkyl group and m and n are 10-90 in the compositional ratio of a copolymer displayed as mol%) are added to and mixed with an aq. soln. of polyvinyl alcohol in a predetermined ratio to prepare a coating soln. for a thermal recording layer. This coating soln. is applied to a support such as paper or a plastic film and dried to obtain a thermal recording material having the thermal recording layer. As a concrete example of the dye precursor, there is a triarylmethane compd. and, as a concrete example of the electron acceptive compd., there is a phenol derivative or an aromatic carboxylic acid derivative.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive recording material, and more particularly to a heat-sensitive recording material excellent in image stability.

[0002]

2. Description of the Related Art A heat-sensitive recording material is generally provided with a heat-sensitive recording layer containing, on a support, an electron-donating, usually colorless or pale-colored dye precursor and an electron-accepting compound (usually called a developer). By heating with a thermal head, a heating pen, a laser beam or the like, a dye precursor and a developer react instantaneously to obtain a recorded image. JP-B-43-41
No. 60, Japanese Patent Publication No. 45-14039 and the like. Such a thermal recording material has the advantages that it can be recorded with a relatively simple device, is easy to maintain, and does not generate noise, and it is used for various measuring recorders, facsimiles, printers, computer terminals. It is used in a wide range of fields such as vending machines, labels and ticket vending machines.

However, as the demand for heat-sensitive recording materials has greatly increased in recent years, it has become a problem that image recording stability is significantly inferior to other recording systems. As the above-mentioned color developer, bisphenol A [2,
2-bis (4-hydroxyphenyl) propane] is used because of its stable quality, low cost, good color development, etc. The image of the heat-sensitive recording material is gradually faded with time even when stored under normal environmental conditions. In addition, white powder is often deposited on the image surface in parallel with fading (normally called powder blowing), and this phenomenon also significantly impairs image quality. For this reason, the current thermosensitive recording has a serious defect as a recording material, because the image becomes difficult to discriminate when stored for a long period of time and may disappear at all in an extreme case. A standard evaluation test item for heat-sensitive recording materials is a storage test under 60 ° C (heat resistance test). However, under these conditions, discoloration is significantly accelerated, and therefore the thermal stability of the color-developing material is high. It is thought that the low value is the cause.

From the above reasons, in order to fix the heat-sensitive recording material in the market in the future and further expand its use, it is necessary to improve the reliability of the recording material by improving the thermal stability of the image and the recording quality. Raising it has become an unavoidable technical issue.

In order to achieve this object, various studies have been conducted in the past, and many proposals have been made regarding a heat-sensitive recording material using a novel developer replacing bisphenol A. There is. For example, JP-A-57-21
0866, 58-82788, 58-1325.
No. 93, No. 59-118491, No. 59-18788
No. 9 and No. 60-13852 disclose arylsulfonylphenol derivatives and JP-A No. 58-119893.
No. 59-169884, a bis (4-hydroxyphenyl) sulfone derivative is proposed. Further, JP-A-4-62091 also proposes a phenol resin (novolac type resin) as a color developer. Further, Japanese Patent Application Laid-Open No. 63-141785 proposes a heat-sensitive recording material using a combination of a polymeric color former and a polymeric developer, and Japanese Patent Application Laid-Open No. 64-53892 discloses a fine particle form. Proposals have been made to use the above polymer compound as a developer, but no polymer compound group found in the present invention as a specific compound is exemplified. The thermal recording materials prepared on the basis of these various proposals are still at an insufficient level in terms of image thermal stability and the above-mentioned recording quality improvement, but are still at an insufficient level, and should be practically satisfactory. The reality is that no kimono has been obtained.

[0006]

The object of the present invention is to obtain excellent thermal stability and recording quality of an image by using a specific phenolic polymer compound as an electron-accepting compound, and further, to improve dusting and color development. The purpose of the present invention is to obtain a heat-sensitive recording material having a satisfactory level of properties such as white background coloring.

[0007]

A heat-sensitive recording material containing a usually colorless to light-colored dye precursor and an electron-accepting compound which reacts with heating to develop the dye precursor,
By incorporating the polymer copolymer represented by Chemical Formula 1 as the electron-accepting compound, the image has excellent thermal stability and recording quality, and is also satisfactory in properties such as dusting, coloring, and white background coloring. It was possible to obtain a heat-sensitive recording material at a proper level.

As is clear from Chemical formula 1, the polymer compound of the present invention is characterized in that it is a copolymer of p-vinylphenol and a p-substituted styrene derivative. A homopolymer of p-vinylphenol can also be used as an electron-accepting compound having excellent image stability, but this time, it was found that when it is copolymerized with a styrene derivative having a specific substituent, the coloring property is further improved. Completed the invention. The result that the coloring property is improved, though the density of the phenolic hydroxyl group in the molecule is remarkably reduced by the copolymerization, is extremely unexpected.

In the chemical formula 1, R represents an alkyl group, an alkenyl group or an aralkyl group which may have a substituent. m and n represent the composition ratio of the copolymer expressed in mol%, and m and n are 10 to 90.

When R further has a substituent, examples of the substituent include an alkyl group, an aryl group, an alkoxy group and an aryloxy group.

When m is smaller than 10 or larger than 90, the color developability is deteriorated in both cases, which is not preferable. There is no particular limitation as long as it is in the range of 10 to 90, but normally it is preferably in the range of 30 to 80.

The polymer compound of the present invention comprises a third compound other than the repeating unit shown in Chemical formula 1 within a range not departing from the object of the present invention.
It may contain components. The polymer compound of the present invention may be used alone or in combination of two or more.

Specific examples of the polymer compound of the present invention will be given below, but the present invention is not limited thereto. p-Vinylphenol / p-methoxystyrene copolymer (m = 75) p-vinylphenol / p-methoxystyrene copolymer (m = 50) p-vinylphenol / p-methoxystyrene copolymer (m = 25) ) P-vinylphenol / p-ethoxystyrene copolymer (m = 70) p-vinylphenol / p-isopropoxystyrene copolymer (m = 65) p-vinylphenol / p- (2-ethoxyethoxy)
Styrene copolymer (m = 75) p-vinylphenol / p- (3-phenoxypropoxy) styrene copolymer (m = 70) p-vinylphenol / p-allyloxystyrene copolymer (m = 65) p -Vinylphenol / p-methacryloxystyrene copolymer (m = 70) p-vinylphenol / p-benzyloxystyrene copolymer (m = 85) p-vinylphenol / p-benzyloxystyrene copolymer (m = 50) p-vinylphenol / p- (o-methylbenzyloxy) styrene copolymer (m = 80) p-vinylphenol / p- (p-methylbenzyloxy) styrene copolymer (m = 45) p -Vinylphenol / p- (p-chlorobenzyloxy) styrene copolymer (m = 40) p-Vinylphenol / p- (2- Eniruetokishi)
Styrene copolymer (m = 65)

The polymer compound of the present invention can be produced by copolymerizing vinylphenol and substituted styrene by a method well known in the art. It can be easily obtained by using a homopolymer as a raw material and etherifying a part of the phenolic hydroxyl group by a polymer reaction. That is, in order to produce the copolymer of the present invention, it is not necessary to synthesize a special styrene derivative, and it may be derived from an inexpensive commercially available polymer, which is extremely advantageous in terms of production cost.

Next, a specific method for producing the heat-sensitive recording material according to the present invention will be described. The heat-sensitive recording material according to the present invention generally comprises, on a support, an electron-donating, usually colorless or light-colored dye precursor and an electron-accepting compound as main components, and these are dispersed and coated in a binder to form a heat-sensitive recording layer. By heating with a thermal head, a heating pen, a laser beam or the like, a dye precursor and an electron-accepting compound react instantaneously to obtain a recorded image. JP-B-43-4160 and JP-B-45-
No. 14039 is disclosed. Further, a pigment, a sensitizer, an antioxidant, an anti-sticking agent, etc. are added to the heat-sensitive recording layer as needed.

The dye precursor used in the heat-sensitive recording material of the present invention is not particularly limited as long as it is generally used for pressure-sensitive recording paper or heat-sensitive recording paper.

Specific examples are as follows: (1) Triarylmethane compound: 3,3-bis (p
-Dimethylaminophenyl) -6-dimethylaminophthalide (crystal violet lactone), 3,3-bis (p-dimethylaminophenyl) phthalide, 3- (p
-Dimethylaminophenyl) -3- (1,2-dimethylindol-3-yl) phthalide, 3- (p-dimethylaminophenyl) -3- (2-methylindole-3-
Yl) phthalide, 3- (p-dimethylaminophenyl)
-3- (2-phenylindol-3-yl) phthalide, 3,3-bis (1,2-dimethylindole-3-
Yl) -5-dimethylaminophthalide, 3,3-bis (1,2-dimethylindol-3-yl) -6-dimethylaminophthalide, 3,3-bis (9-ethylcarbazol-3-yl) -5-dimethylaminophthalide,
3,3-bis (2-phenylindol-3-yl)-
5-dimethylaminophthalide, 3-p-dimethylaminophenyl-3- (1-methylpyrrol-2-yl) -6
-Dimethylaminophthalide, etc.

(2) Diphenylmethane compound: 4,
4'-bis (dimethylaminophenyl) benzhydryl benzyl ether, N-chlorophenyl leuco auramine, N-2,4,5-trichlorophenyl leuco auramine, etc.,

(3) Xanthene compound: Rhodamine B
Anilinolactam, Rhodamine B-p-chloroanilinolactam, 3-diethylamino-7-dibenzylaminofluorane, 3-diethylamino-7-octylaminofluorane, 3-diethylamino-7-phenylfluorane, 3-diethylamino -7-Chlorofluorane, 3
-Diethylamino-6-chloro-7-methylfluorane, 3-diethylamino-7- (3,4-dichloroanilino) fluorane, 3-diethylamino-7- (2-chloroanilino) fluorane, 3-diethylamino-6-
Methyl-7-anilinofluorane, 3- (N-ethyl-
N-tolyl) amino-6-methyl-7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3- (N-ethyl-N-tolyl) amino-6-
Methyl-7-phenethylfluorane, 3-diethylamino-7- (4-nitroanilino) fluorane, 3-dibutylamino-6-methyl-7-anilinofluorane, 3
-(N-methyl-N-propyl) amino-6-methyl-
7-anilinofluorane, 3- (N-ethyl-N-isoamyl) amino-6-methyl-7-anilinofluorane, 3- (N-methyl-N-cyclohexyl) amino-
6-methyl-7-anilinofluorane, 3- (N-ethyl-N-tetrahydrofuryl) amino-6-methyl-7
-Anilino Fluoran, etc.

(4) Thiazine-based compounds: benzoyl leuco methylene blue, p-nitrobenzoyl leuco methylene blue, etc.

(5) Spiro compounds: 3-methylspirodinaphthopyran, 3-ethylspirodinaphthopyran,
3,3′-dichlorospirodinaphthopyran, 3-benzylspirodinaphthopyran, 3-methylnaphtho- (3-methoxybenzo) spiropyran, 3-propylspirobenzopyran, and the like, which may be used alone or in combination with 2 It can be used by mixing more than one species.

The compound of the present invention can be used in combination with other electron-accepting compound. In this case, the electron-accepting compound may be any acidic substance generally used in heat-sensitive recording materials, and examples thereof include polyvalent metals such as phenol derivatives, aromatic carboxylic acid derivatives, aryl-substituted thiourea derivatives, and zinc salts of organic compounds. Salts can be used.

As the binder used in the heat-sensitive recording material, starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, polyvinyl alcohol, modified polyvinyl alcohol, polyacrylic acid soda, acrylic acid amide / acrylic acid ester copolymer. , Acrylic acid amide / acrylic acid ester / methacrylic acid terpolymer, styrene / maleic anhydride copolymer alkali salt, ethylene /
Water-soluble adhesive such as alkali salt of maleic anhydride copolymer, polyvinyl acetate, polyurethane, polyacrylic acid ester, styrene / butadiene copolymer, acrylonitrile / butadiene copolymer, methyl acrylate / butadiene copolymer, Examples include latex of ethylene / vinyl acetate copolymer and the like.

Further, as a sensitizer for further improving the sensitivity, waxes such as N-hydroxymethylstearic acid amide, stearic acid amide and palmitic acid amide, naphthol derivatives such as 2-benzyloxynaphthalene, p-benzyl and the like. Biphenyl derivatives such as biphenyl and 4-allyloxybiphenyl, 1,2-bis (3-methylphenoxy) ethane, 2,2′-bis (4-methoxyphenoxy) diethyl ether, bis (4-methoxyphenyl) ether, etc. A polyether compound, carbonic acid such as diphenyl carbonate, oxalic acid dibenzyl, oxalic acid bis (p-methylbenzyl) ester, or an oxalic acid diester derivative can be used in combination.

Examples of the pigment include diatomaceous earth, talc, kaolin, calcined kaolin, calcium carbonate, magnesium carbonate, titanium oxide, zinc oxide, silicon oxide, aluminum hydroxide and urea-formalin resin.

In addition, for the purpose of preventing head wear and sticking, higher fatty acid metal salts such as zinc stearate and calcium stearate, waxes such as paraffin, oxidized paraffin, polyethylene, oxidized polyethylene, stearic acid amide, caster wax, etc., , Dispersants such as sodium dioctyl sulfosuccinate, UV absorbers such as benzophenone-based and benzotriazole-based,
Furthermore, a surfactant, a fluorescent dye, etc. are added as needed.

Paper is mainly used as the support used in the present invention, but a non-woven fabric, a plastic film, a synthetic paper, a metal foil, or a composite sheet in which these are combined can be optionally used. In addition, an overcoat layer may be provided to protect the heat-sensitive recording layer, or an undercoat layer composed of a single layer or a plurality of layers of pigments or resins may be provided between the heat-sensitive recording layer and the support to produce a heat-sensitive recording material Various known techniques in the art can be used.

The smear amount of the heat-sensitive recording layer is determined by the amounts of the dye precursor which is the color-forming component and the color developer, and usually the dye smear amount of 0.
1 to 1.0 g / m ² is suitable. The polymer compound of the present invention is added in an amount of 5 to 400% by weight, preferably 20 to 300% by weight, based on the dye precursor.

[0029]

EXAMPLES Next, the present invention will be described in more detail by way of examples. The parts and% shown below are based on weight.

<Synthesis Example 1> p-vinylphenol / p-methoxystyrene copolymer
( M = about 75) Synthetic p-vinylphenol homopolymer (Marka Linker M
S-2: 12 g of Maruzen Petrochemical Co., Ltd. was dissolved in 120 ml of methanol, and 4.9 g of 28% methanol solution of sodium methylate was added little by little. As it is 1
After continuing stirring for an hour, 3.2 g of dimethyl sulfate under water cooling
20 ml of methanol solution of was added dropwise over about 2 hours.
After the dropping was completed, the mixture was heated under reflux for about 6 hours. After about half the amount of methanol was distilled off under reduced pressure, the mixture was poured into a slightly acidified water with a small amount of hydrochloric acid to precipitate a crude polymer. The crude polymer obtained was purified by repeating reprecipitation twice. Yield 11.6g.

<Synthesis Example 2> p-Vinylphenol / p-benzyloxystyrene
Synthesis of polymer (m = about 65) P-vinylphenol homopolymer (Marker Linker M
・ S-2: 12 g of Maruzen Petrochemical Co., Ltd. was dissolved in 120 ml of n-propanol, and 2 g of sodium methylate was added.
7.0 g of 8% methanol solution was added little by little. After continuing stirring for 1 hour, methanol was distilled off under reduced pressure. Then, a solution of 6.0 g of benzyl bromide in 30 ml of n-propanol was added dropwise over about 30 minutes. After completion of the dropping, the mixture was heated under reflux for 24 hours. After about half the amount of the solvent was distilled off under reduced pressure, the residue was poured into slightly acidified water with a small amount of hydrochloric acid to precipitate a crude polymer. The crude polymer obtained was purified by repeating reprecipitation twice. Yield 14.2g.

Example 1 (A) Preparation of heat-sensitive coating liquid 3-dibutylamino-6-methyl-7 which is a dye precursor
35 parts of anilinofluorane were pulverized with 70 parts of 2.5% aqueous solution of polyvinyl alcohol in a ball mill for 24 hours to obtain a dye dispersion liquid. Then, 50 parts of the compound obtained in Synthesis Example 1 above was added to a 2.5% polyvinyl alcohol aqueous solution 120.
And a ball mill for 24 hours to obtain a dispersion of the compound of the present invention. Further, 60 parts of 2-benzyloxynaphthalene was ground together with 140 parts of a 2.5% aqueous polyvinyl alcohol solution by a ball mill for 24 hours to obtain a sensitizer dispersion liquid. After mixing these three types of dispersions, the following components were added with stirring and mixed well to prepare a heat-sensitive coating liquid. Calcium carbonate 40% aqueous dispersion 200 parts Polyvinyl alcohol 10% aqueous solution 250 parts Zinc stearate 40% aqueous dispersion 50 parts Water 520 parts

(B) Preparation of heat-sensitive coated paper A base solution having a basis weight of 40 g / m ² is coated with a coating solution having the following composition so that the solid content is 9 g / m ² , dried, and heat-sensitive coated. I made engineering paper. Calcined kaolin 100 parts Styrene-butadiene latex 50% aqueous dispersion 24 parts Water 200 parts

(C) Preparation of heat-sensitive recording material The heat-sensitive coating solution prepared in (A) was smeared on the surface of the heat-sensitive coated paper prepared in (B) so that the solid content was 5.4 g / m ^2. Then, it was dried to prepare a heat-sensitive recording material.

Example 2 A thermosensitive recording material was prepared in the same manner as in Example 1 except that the compound obtained in Synthesis Example 2 was used in place of the compound of Synthesis Example 1 in Example 1.

Example 3 Example 3 was repeated except that p-vinylphenol / p- (3-phenoxypropoxy) styrene copolymer (m = about 30) was used in place of the compound of Synthesis Example 1 in Example 1. Example 1
A heat-sensitive recording material was prepared in the same manner as in.

Comparative Example 1 A thermosensitive recording material was prepared in the same manner as in Example 1 except that bisphenol A was used instead of the compound of Synthesis Example 1 in Example 1.

Comparative Example 2 Instead of the compound of Synthesis Example 1 in Example 1, a homopolymer of p-vinylphenol (marker linker M.S-
2: A thermal recording material was prepared in exactly the same manner as in Example 1 except that Maruzen Petrochemical Co., Ltd. was used.

"Evaluation" Examples 1 to 3 and Comparative Examples 1 to 1
The heat-sensitive recording material obtained in No. 2 was calendered so that the Bekk smoothness of the heat-sensitive coated surface was 400 to 500 seconds, and then a printing test was performed using a thermal tilt tester manufactured by Toyo Seiki Seisakusho. Heating temperature 150 ° C, heating time 1 second, pressure 1
Printed under the condition of Kg / cm ² and the color density is Macbeth RD-91.
It measured with the 8 type reflection densitometer.

Next, in order to evaluate the thermal stability, an accelerated test was carried out in which the printed sample obtained above was stored for 3 days in a thermostat controlled at 60 ° C. Then, the thermal stability was evaluated by comparing the color density after storage and the white background color density with the initial values. Regarding the evaluation of powder blowing, the sample after the above test was visually observed for the degree of whitening of the image area due to the deposition of white powder, and judged (○: no whitening was observed, ×: large whitening was observed. ).

The results are shown in Table 1.

[0042]

[Table 1]

[0043]

As is clear from the examples, the heat-sensitive recording material of the present invention which uses a specific vinylphenol polymer compound as an electron-accepting compound is excellent in thermal stability of images and recording quality, and It can be seen that the heat-sensitive recording material has extremely high utility value, which is at a satisfactory level with respect to properties such as powder blowing, color developability and white background coloring.

Claims (1)

[Claims] 1. A heat-sensitive recording material containing a usually colorless to light-colored dye precursor and an electron-accepting compound that reacts when heated to develop the color of the dye precursor, wherein the electron-accepting compound is represented by the following chemical formula 1. A heat-sensitive recording material containing a polymer compound as described above. [Chemical 1] (R represents an alkyl group, an alkenyl group or an aralkyl group which may have a substituent. M and n represent the composition ratio of the copolymer expressed in mol%, and m and n are 10 to 90. .)