JPH0421487A - Thermal recording body - Google Patents

Abstract

PURPOSE:To obtain superior color forming properties, prevent a background fog in the storage under a high-temperature and -humidity condition or a high- temperature condition, and enhance the stability of a recording part by using 4-hydroxy-4'-isopropyloxy diphenylsulfone and/or 4-4'-thiobis(6-t-butyl-m-cresol) as a color developer and using di(p-methybenzyl)oxalate as a hot melting substance. CONSTITUTION:A leuco compound is a colorless or light-colored substance reacting with an organic acid to produce a color. The leuco compound is preferably incorporated in the amount of 1-20wt.%, pref. 5-15wt.%, of all the solid content. As a color developer, 4-hydroxy-4'-isopropyloxy diphenylsulfone and/or 4-4'-thiobis(6-t-butyl-m-cresol) is used. The color developer is preferably incorporated in the amount of 1-50%, pref. 5-40wt.%, of all the solid content. As a color-forming accelerator, bis(p-methybenzyl)oxalate is used in the amount of 1-50%, pref. 5-40%, of all the content.

Description

[Detailed Description of the Invention] (Industrial Application Field) The invention combines a colorless or light-colored organic dye, generally called a leuco compound, and an organic acid such as a phenol compound that develops a color by reacting with the leuco compound. This invention relates to improvement of a heat-sensitive recording material having the main component.

(Prior Art) A thermosensitive recording material containing a leuco compound and an organic acid is already known, for example, from Japanese Patent Publication No. 14039/1983. This recording paper applies thermal energy to the recording layer to soften or melt the leuco compound, organic acid, and binder.
It is based on the principle of bringing both color components into contact and causing a color reaction, and has recently been used in various fields such as printers and facsimile machines. The recording characteristics of this recording paper vary depending on the application, but in order to increase the recording speed, for example, it is necessary to improve the sample recording device and to promote the color development of the recording medium itself. The items required for a thermosensitive recording medium are as follows.

(1) The color density and sensitivity are sufficient.

(2) The fastness of the recorded area after color development is sufficient.

(3) White parts do not develop color due to fingerprints or external conditions such as temperature and humidity.

Furthermore, as a method for promoting color development, a method is generally used in which a low melting point substance is included in the recording layer. As a low melting point substance, i.e. a color accelerator or a sensitizer,
-4160, urea, phthalic anhydride, and acetanilide, and JP-A-48-19231, paraffin wax, carnauba wax, beeswax, wood wax, higher fatty acids, and higher fatty acid esters, and JP-A-49-1774.
According to Publication No. 8, salicylic acid, anisic acid, phthalic acid monophenyl ester, and phthalic acid monobenzyl ester are used, and in recent years, fatty acid amides have also been widely used as color accelerators. That is, Japanese Patent Publication No. 51-27599 describes the sensitizing effect of fatty acid amide by combining paraffin or microcrystalline wax with fatty acid amide, and Japanese Patent Publication No. 54-139740 also describes the sensitizing effect of fatty acid amide using a combination of paraffin or microcrystalline wax and fatty acid amide. The sensitizing effect of fatty acid amides has been described and is well known.

Furthermore, JP-A No. 57-27785 discloses para-benzylbiphenyl, and JP-A No. 60-82382 discloses para-benzylbiphenyl.

Conventionally, 2,2-bis (4-
Hydroxyphenyl)propane (bisphenol A) and benzyl 4-hydroxybenzoate are in practical use, but bisphenol A does not have a sufficient color development rate (benzyl 4-hydroxybenzoate has a good color development rate but does not develop color. It has a significant drawback of the so-called "whitening phenomenon" in which the parts become white and the color becomes lighter over time.

The use of 4-hydroxy-4'-isopropyloxydiphenyl sulfone as a color developer is disclosed in JP-A-60-1.
It is disclosed in Japanese Patent No. 3852.

However, by simply using 4-hydroxy-4'-isopropyloxydiphenyl sulfone as a color developer, it was possible to obtain almost the same coloring characteristics as bisphenol A, although there was no whitening phenomenon.

Therefore, a combination of 4-hydroxy-4'-isopropyloxydiphenyl sulfone and a color accelerator was proposed in JP-A-62
This method is disclosed in Japanese Patent Publication No. 130878, Japanese Patent Application Laid-Open No. 281670, and the like. However, even when using 4-hydroxy-4'-isopropyloxydiphenyl sulfone and these disclosed color accelerators, excellent color development properties can be obtained, and furthermore, when stored under high temperature, high humidity, or high temperature conditions, there will be no fogging on the background or damage to the recording area. I haven't been able to find anything that satisfies stability at the same time.

Furthermore, JP-A-2-25377 discloses a heat-sensitive recording material containing bis(p-methylbenzyl) sinioate as a color development accelerator, but even this has insufficient storage stability and fingerprint resistance. There wasn't.

(Problems to be Solved by the Invention) The present invention provides a heat sensitive film that simultaneously satisfies the characteristics of superior color development, no background fogging when stored under high temperature, high humidity, or high temperature conditions, and high stability of the recording area. The purpose is to provide a record.

(Means for Solving the Problems) According to the present invention, 4-hydroxy-4'-isopropyloxydiphenyl sulfone and/or 4-4 as a color developer
A heat-sensitive recording material having excellent heat-sensitive properties and storage stability by using '-thiobis(6-t-butyl-m-cresol) and di(p-methylbenzyl) sinioate as a thermofusible substance. was gotten.

The leuco compounds used in the present invention are colorless to light-colored substances that develop color by reacting with organic acids. Examples include various derivatives such as phenoxazine-based, phenoxazine-based, spiropyran-based, indoline-based, and indigo-based. Preferred leuco compounds include, for example, 3-diethylamino-6-methyl-7-anilinofluorane, 3-
(N-ethyl-P-)luidino)-6-methyl-7-anilinofluorane, 3-jethylamino-6-methyl-
7-(ortho, para-dimethylanilino)fluorane,
3-Piperidino-6-methyl-7-anilinofluorane, 3-(N-cyclohexyl-N-methylamino)-
6-Methyl 7-anilinofluorane, 3-diethylamine-7-(ortho-chloroanilino)fluorane, 3-
Diethylamino-7-(meta-trifluoromethylanilino)fluorane, 3-diethylamine-6-methyl-
Chlorofluorane, 3-diethylamine-6-methyl-
Examples include fluoran, 3-(N-isoamyl-N-ethylamino)-6-methyl-7-anilinofluoran, and 3-dibutylamino-6-methyl-7-anilinofluoran.

The leuco compound is 1 to 20% by weight of the total solid content of the heat-sensitive recording layer.
(hereinafter abbreviated as %), preferably 5 to 15%.

In the present invention, 4-hydroxy-4'-isopropyloxydiphenyl sulfone and/or 4,4'
- Thiobis(6-t-butyl-m-cresol) is used. The color developer should be used in an amount of 1 to 50%, preferably 5 to 40%, of the total solid content of the heat-sensitive recording layer.

Further, the present invention is characterized in that bis(p-methylbenzyl) oxalate is used as a color development accelerator. The color development accelerator accounts for 1 to 50% of the total solid content of the heat-sensitive recording layer, preferably 5 to 50%.
A good value is 40%.

The binder used in the present invention mainly consists of a water-soluble binder, which releases and fixes the coloring agent dispersed in fine particles to each other. Polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, Examples include acrylic acid, casein, gelatin, starch and derivatives thereof. The content of these binders is preferably 1 to 35%, preferably 10 to 30%, of the total solid content of the heat-sensitive recording layer.

The heat-sensitive recording layer of the present invention may contain other additives as necessary, such as inorganic or organic pigments such as clay, calcium carbonate, synthetic silica, aluminum hydroxide, talc, titanium oxide, and zinc oxide, waxes, and anti-stick additives. Various fatty acid metal salts for water resistance, water resistance agents for water resistance improvement, phenol resins, surfactants, etc. can be added.

In addition, various antioxidants and ultraviolet absorbers can be added for storage stability.
．． 1. 3-1-Lis(2-methyl-4-hydroxy-5-cyclohexylphenyl)butane, 1,1.3-
) Lis (2-methyl-4hydroxy-3-tert-
Hindered phenyl compounds such as (butylphenyl)butane are preferred.

The paint for the heat-sensitive recording layer of the present invention is prepared by separately adding the above-mentioned leuco compound and color developer to bis(p-methylbenzyl oxalate).
and, if necessary, additives such as pigments and sensitivity adjusters, were pulverized and dispersed in an aqueous medium containing a binder such as polyvinyl alcohol at an appropriate concentration using a pulverizer such as a ball mill or a sand grinder. After that, it is generally prepared by mixing and stirring the dye dispersion and the organic acid dispersion. It is advantageous in terms of color development efficiency to make each constituent substance as fine as possible, and it is preferable to make it fine to branch threads of 0.5 to 3 μm. The heat-sensitive paint thus obtained is applied to the support described below and dried to obtain the heat-sensitive recording material of the present invention.

Coating can be performed using a conventional blade coater, air knife coater, bar coater, or reverse roll coater.

In the heat-sensitive recording material of the present invention, an intermediate layer using an inorganic pigment such as calcined kaolin or silica or an organic pigment such as a plastic pigment may be provided between the support and the heat-sensitive recording layer, if necessary. An overcoat layer can also be provided.

As the support used in the present invention, papers such as wood-free paper, medium-quality paper, and coated paper are generally used, but other glass fiber sheets, plastic sheets, film-laminated papers, etc. can also be used as supports. be able to.

(Effects) According to the present invention, a heat-sensitive recording material having excellent color development properties, moisture resistance, heat resistance, and fingerprint resistance is provided.

(Example) Example 1 Solutions A, B and C having the following compositions were prepared.

[Liquid A]

Black leuco dye 3-(N-ethyl-N-isoamyl)amino-6-methyl-7-anilinofluorane [S-
205 Yamada Chemical] 9 parts by weight 12% polyvinyl alcohol aqueous solution 15 parts by weight polystyrene ammonium acrylate 20% aqueous solution
0.7 parts by weight water
30 parts by weight [Liquid B] 4-hydroxy-4'-isopropyloxydiphenyl sulfone 20 parts by weight 12% polyvinyl alcohol aqueous solution 33.3 parts by weight polystyrene ammonium acrylate 20% aqueous solution
1.6 parts by weight 1.1.3-
) Lis(2-methyl-4-hydroxy-5-cyclohexylphenyl)butane 4 parts by weight Water 66.7 parts by weight [C
Liquid] 20 parts by weight of bis(P-methylbenzyl oxalate), 11 ff, 12% aqueous solution of polyvinyl alcohol, 33.3 parts by weight, 20% aqueous solution of polystyrene ammonium acrylate
1.6 parts by weight water
A component of 66.7 parts by weight or more was separately dispersed using a sand grinder until the average particle size was 2 μm or less.

Next, Solution D was prepared.

[Liquid D]

Non-quality silica [Mizukasil P-527 manufactured by Mizusawa Chemical Industry]
20 parts by weight water
80 parts by weight of the liquid was dispersed for 10 minutes using a homomixer.

54.7 parts by weight of liquid A prepared as above, 1 part of liquid B
25.6 parts by weight, 121.6 parts by weight of liquid C, and 100 parts by weight of liquid D.
30% zinc stearate to this mixed solution.
33.3 parts by weight of a dispersion (D-523 manufactured by Middle East Yushi) and 100 parts by weight of a 12% polyvinyl alcohol aqueous solution were added and stirred to prepare a heat-sensitive coating liquid.

This heat-sensitive coating liquid was applied to high-quality paper with a drying weight of 5 Qg/m' and dried, and then calendered to give a heat-sensitive recording surface with a Beck smoothness of 600 seconds. Obtained a record.

Example 2 Completely the same as Example 1 except that 4-hydroxy-4'-isoprobyloxydiphenyl sulfone in Solution B was replaced with 447-thiobis(6-t-butyl-m-cresol). A thermosensitive recording material was obtained.

Example 3 In Example 1, 3-(N-ethyl-N-isoamyl)amino-6-methyl-7-anilinofluorane in Solution A was replaced with 3-dibutylamino-6-methyl-7-anilinofluorane. A thermosensitive recording material was obtained in exactly the same manner as in Example 1 except that .

Comparative Example 1 A thermosensitive recording material was obtained in exactly the same manner as in Example 1 except that Liquid C was not used in Example 1.

Comparative Example 2 A thermosensitive recording material was obtained in exactly the same manner as in Example 1, except that dibenzyl oxalate was used in place of di(P-methylbenzyl oxalate) in Liquid C in Example 1.

Comparative Example 3 A thermosensitive recording material was obtained in exactly the same manner as in Example 1 except that di(P-methylbenzyl oxalate) in Solution C was replaced with stearamide.

Comparative Example 4 A thermosensitive recording material was obtained in exactly the same manner as in Example 1 except that 4-hydroquine-4'-isopropyloxydiphenyl sulfone in liquid B was replaced with benzyl p-oxybenzoate.

Comparative Example 5 A thermosensitive recording material was obtained in exactly the same manner as in Example 1 except that bisphenol A was used in place of 4-hydroxy-4' isopropyloxydiphenyl sulfone in the B solution.

Comparative Example 6 A thermosensitive recording material was obtained in exactly the same manner as in Example 1, except that 4-phenylphenol was used in place of 4-hydroxy-4'isopropyloxydiphenylsulfone in Solution B.

Comparative Example 7 A thermosensitive recording material was obtained in exactly the same manner as in Example 1 except that 4-benzylbiphenyl was used in place of di(P-methylbenzyl oxalate) in Liquid C.

The following evaluations were performed on the heat-sensitive recording bodies obtained in Examples 1 to 3 and Comparative Examples 1 to 7. The results are shown in Table-1.

(1) Color development properties were evaluated using a heat-sensitive tester TH-PMDC (manufactured by Daiyo Denki Co., Ltd.). The printing conditions were as follows.

Thermal head: KJT-256-8MGFI (Kyocera!) Applied voltage: 24.OV Pulse period: 2.Qmsec Pulse time: l, 2m5ec and 1.6m5e
c Background and recording density were measured using Macbeth RD-514.

The recording part of the heat-sensitive recording medium used for the storage test had a pulse time of 1
．． The one printed at 6m5ec was used.

(2) Fingerprint resistance: Attach fingerprints to the colored image and white area and store at room temperature and humidity for 30 minutes.
Stored for days. After storage, the degree of discoloration and color development of the recording area and white area was examined.

Good: ◎, Fair; O9 poor: × (3) Heat resistance It was stored under high temperature dry conditions of 60°C for 24 hours, and the density of the recorded area and white area after storage was measured using a Macbeth densitometer RD514.

(4) Humidity resistance It was stored under high temperature conditions of 40° C.-90% RH for 24 hours, and the recorded area and white area after storage were measured using a Macbeth densitometer RD514.

Claims (1)

[Claims] In a heat-sensitive recording material in which a heat-sensitive recording layer containing a colorless to light-colored leuco compound and a color developer that develops a color upon contact with the leuco compound is provided on a support, 4-hydroxy-4' is used as the color developer. -isopropyloxydiphenylsulfone and/or 4,4'-thiobis(6-t-butyl-m
-cresol) and contains di(p-methylbenzyl oxalate) as a color development accelerator.