JPH04144787A - Thermal recording material - Google Patents

Abstract

PURPOSE:To obtain a thermal recording material of which fading of an image part is never generated even in high temperature and high humid environment by a method wherein a specific block isocyanate compound is used as a developer. CONSTITUTION:A thermal recording material is formed by providing a thermal coloring layer containing a colorless or light colored dye precursor and a developer coloring it by reaction therewith under heating to at least, one surface of a sheetlike substrate. In that case, the developer is a block isocyanate compound to be obtained by reaction of 3, 4-dichlorophenyl-isocyanate with phenol compound. As the block isocyanate compound, that expressed by the formula I (where R represents phenol compound residual radical and n represents an integer of 1-4 in the formula) should be preferable. Those isocyanate compounds are manufactured by thermal reaction in inactive solvent of a specific isocyanate compound with equivalent phenol compound as a blocking agent. At that time, a catalyst may be used if necessary.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a heat-sensitive recording medium, and in particular, it has high whiteness, high sensitivity, excellent solvent resistance in the white background area, and good resistance in the image area. The present invention relates to a heat-sensitive recording material having excellent heat-resistant storage properties and moisture-resistant storage properties.

[Conventional technology]

Conventional heat-sensitive recording materials utilize a heat-generating color reaction between colorless or light-colored leuco dyes and phenols or organic acids.
Special Publication No. 43-4160, Special Publication No. 45-14039,
It is disclosed in Japanese Patent Publication No. 48-27736, etc.
And it has been widely put into practical use. In recent years, such heat-sensitive recording materials have been developed to form colored images simply by heating them, allow for relatively compact recording devices, are easy to maintain, and do not generate noise. Due to its advantages, it is widely used as various information recording materials such as facsimiles, computer output machines, labels, automatic ticket vending machines, CD-ATMs, order slip output machines for family restaurants, data output machines for scientific research equipment, and printers. has been done. With the expansion of the range of applications of such heat-sensitive recording materials, there are increasing opportunities for heat-sensitive recording materials to come into contact with cosmetic creams and solvents, and to be exposed to harsh conditions such as high temperature and high humidity. For example, as a color developer conventionally used, 4,4'-isopropylidene biphenol or benzyl p-hydroxybenzoate (JP-A-52-14
No. 0483), etc., color may develop in the white background due to the adhesion of solvent, or the colored image may be exposed to high temperature or heat.
When placed under high humidity, problems such as fading of the image area occur.

[Problems to be Solved by the Invention] The present invention has high whiteness, high sensitivity, does not cause color development in the white background even when solvent is attached, and can be used even in high temperature and high humidity environments. It is an object of the present invention to provide a heat-sensitive recording material that does not cause color fading in the image area.

[Means to solve the problem]

In order to solve the above-mentioned problems, the present inventors have conducted intensive research and found that the above-mentioned problems can be solved by using a specific blocked isocyanate compound as a color developer. completed.

The heat-sensitive recording material according to the present invention includes a sheet-like substrate and a color developer that is formed on at least one surface of the sheet-like substrate and reacts with a colorless or light-colored dye precursor under heating to develop color. a thermosensitive color forming layer, the color developer is 3
．． It is characterized by containing a blocked isocyanate compound obtained by the reaction of 4-dichlorophenylisocyanate and a phenol compound.

By using the specific blocked isocyanate compound mentioned above as a color developer, it has high whiteness and high sensitivity, does not cause color development on the white background even when solvent is attached, and can be used at high temperatures and high temperatures. It is possible to obtain a thermosensitive recording material with high shelf life, which does not cause discoloration of the image area even under humid conditions.

A heat-sensitive recording material using a blocked isocyanate compound obtained by the reaction of an isocyanate compound and a phenol compound as a color developer is disclosed in JP-A-60-184879, but this is simply a matter of fogging the white background. It is merely characterized by the suppression of phenomena. In contrast, the present inventors have found that 3.4-
By selecting dichlorophenyl isocyanate and using a blocked isocyanate compound obtained by reacting it with a phenol compound as a color developer, it has high whiteness and high sensitivity, and there is no coloration in the white background due to solvent adhesion. It was discovered that a heat-sensitive recording material having excellent heat-resistant storage stability and moisture-resistant storage stability in the image area can be obtained, and based on this knowledge, the present invention was completed.

The blocked isocyanate compound used in the present invention is represented by the following general formula (■): (However, in the above formula, R represents a phenol compound residue, and n represents an integer from 1 to 4.) is preferred.

These blocked isocyanate compounds are produced by thermally reacting a specific isocyanate compound and an equivalent amount of a phenol compound as a blocking agent in an inert solvent. At this time, it is also possible to use a catalyst if necessary.

The phenol compound used to obtain the blocked isocyanate compound represented by general formula (n) is, for example,
Phenol, p-methylphenol, m-methylphenol, 0-methylphenol, p-methoxyphenol, p-chlorophenol, m-chlorophenol, 3.
4-dichlorophenol, 2.4-dichlorophenol, P-phenylphenol, methyl p-hydroxybenzoate, ethyl p-hydroxybenzoate, propyl p-hydroxybenzoate, isopropyl p-hydroxybenzoate, p-hydroxybenzoic acid Butyl, benzyl p-hydroxybenzoate, 4-hydroxy-4'-isoprobyloxydiphenyl sulfone, 1,1-bis(4-hydroxyphenyl)cyclohexane, 7-bis(hydroxyphenylthio)-3,5-dioxa Hebutane, 2.2
-bis(p-hydroxyphenyl)propane, 1.1-
Bis(p-hydroxyphenyl)propane, bis(4-
hydroxyphenyl) sulfone, 4,4'thiobis(p
-hydroxyphenol).

In the heat-sensitive recording material of the present invention, the color developer is contained in the heat-sensitive color forming layer together with a dye precursor such as a leuco dye. The amount of the color developer compound used in the present invention is preferably 10 to 1000% by weight, more preferably 50 to 300% by weight based on the weight of the dye precursor.

The dye precursor used with the color developer compound of the present invention can be selected from those conventionally used as heat-sensitive materials, such as crystal violet lactone, 3
-(N-ethyl-N-isopentylamino)-6-methyl-7-anilinofluorane, 3-diethylamino-6
-Methyl-7-anilinofluorane, 3-diethylamino-6methyl-7-(o,p-dimethylanilino)fluorane, 3-(N-ethyl-P-toluidino)-6-methyl-7-anilinofluoran Oran, 3-pyrrolidino-6-
Methyl-7-anilinofluorane, 3-dibutylamino-6-methyl-7-anilinofluorane, 3-(N-cyclohexyl-N-methylamino)-6-methyl-7-
Anilinofluorane, 3-diethylamino-7-(0-
chloroanilino)fluoran, 3-diethylamino-7
(m-trifluoromethylanilino)fluorane, 3-
diethylamino-6-methyl-7-chlorofluorane,
3-diethylamino-6-methylfluorane and 3-
Examples include cyclohexylamino-6-chlorofluoran. These dye precursors may be used alone or in combination of two or more thereof.

The thermochromic layer may also optionally contain a group of thermofusible aromatic organic compounds known as sensitizers.
Examples include 1-hydroxy 2-naphthoic acid phenyl ester (JP 57-191089), p-benzylbiphenyl (JP 60-82382), benzylnaphthyl ether (JP 58-87094). , dibenzyl terephthalate (JP-A-58-98285)
, benzyl p-benzyloxybenzoate (JP-A-57
-201691), diphenyl carbonate, ditolyl carbonate (
1.5
-bis(p-methoxyphenoxy)-3-oxapentane (JP-A-62-181183), di(0-chlorobenzyl)adipate (JP-A-63-183878), p
-Toluenesulfoanilide (JP-A-58-211493
), triphenylmethane (JP-A-56-40587), di(p-methylbenzyl oxalate) (JP-A-64-40587),
No. 1583), tribenzylamine (JP-A-58-15)
1296), fluorene (JP-A-53-5636)
, dihydroanthracene (JP-A-59-101392), and 1,4-bis(P-tolyloxy)benzene (JP-A-2-153783).

Further, the heat-sensitive coloring layer preferably contains an inorganic pigment, and may further contain waxes if necessary.

Further, the heat-sensitive coloring layer contains a binder for binding the above-mentioned components and fixing them to the sheet-like substrate. The content of the dye precursor in the thermosensitive color forming layer is generally 5 to 20% by weight, and the content of the color developer is generally 10 to 40% by weight. In addition, the binder content is generally 5 to 20% by weight, and when white pigments and waxes are included, the content is generally 10 to 50% by weight, and 5 to 50% by weight, respectively.
It is about 30% by weight, and when a sensitizer is included, its content is generally about 10 to 40%.

Organic or inorganic pigments used in the heat-sensitive coloring layer include calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, clay, calcined seaweed, talc, and surface-treated pigments. Examples include inorganic fine powders such as calcium carbonate and silica, as well as organic fine powders such as urea-formalin resin, styrene/methacrylic acid copolymer, and polystyrene resin.

Furthermore, the waxes used in the heat-sensitive coloring layer include known waxes such as paraffin, amide wax, bisimide wax, and metal salts of higher fatty acids. The binders include polyvinyl alcohols of various molecular weights, starches and their derivatives, cellulose derivatives such as methoxycellulose, carboxymethylcellulose, methylcellulose, and ethylcellulose, sodium polyacrylate, polyvinylpyrrolidone, and acrylic acid amide/acrylic ester copolymers. In addition to water-soluble polymers such as acrylamide/acrylic ester/methacrylic acid ternary copolymer, styrene/maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate, gelatin, and casein, polyvinyl acetate , polyurethane,
Latex such as styrene/butadiene copolymer, polyacrylic acid, polyacrylic acid ester, vinyl chloride/vinyl acetate copolymer, polybutyl methacrylate, ethylene/vinyl acetate copolymer, styrene/butadiene/acrylic copolymer, etc. Can be used.

A heat-sensitive coloring layer coating solution is prepared by mixing appropriate amounts of each of these components, and this is applied to paper, coated paper whose surface is coated with clay, plastic, etc., or synthetic paper made mainly from plastic. is coated on a plastic film and dried and solidified to produce a heat-sensitive recording material. The coating amount of the coating liquid for the heat-sensitive coloring layer is 1 to 10 g/dry state.
It is preferable to set it so that it becomes rrf, and it is 2 to 7 g.
/rrf is particularly preferred.

The heat-sensitive recording material of the present invention having the above structure has high whiteness and high sensitivity, and is excellent in solvent resistance of the white background area and heat-resistant storage stability and humidity-resistant storage stability of the colored image.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited thereto.

Unless otherwise specified, numbers are in parts by weight.

Moreover, the structures of compounds A-D were identified from nuclear magnetic resonance spectroscopy.

〔Example〕

1. Synthesis of blocked isocyanate compound (A) having the following general formula (N) In order to produce compound (A), 18.3 g of p-hydroxybenzoic acid benzyl ester, 3.4-dichlorophenylisocyanate 15.0 g of Nato was dissolved in 20 d of anhydrous toluene, and this was heated at 110°C for 1 hour.

When the mixture was allowed to cool, crystals precipitated. The crystals were separated by filtration, washed with toluene and hexane, and then purified by recrystallization from ethanol.

White crystal. Melting point: 145°C0■ Preparation of pigmented undercoated paper Add 85 parts of Baked Ray (trade name: Ansilex) to 320 parts of water.
A coating liquid obtained by mixing 40 parts of a styrene-butadiene copolymer emulsion (solid content 50%) and 50 parts of a 10% oxidized starch aqueous solution in the dispersion obtained by dispersing in 48 g/
A pigment undercoated paper was prepared by applying the pigment on rrr base paper so that the coating amount after drying was 7.0 g/rd.

■ Preparation of dye precursor dispersion A A dispersion liquid having the following composition was prepared by a conventional method.

10% polyvinyl alcohol solution 10% water
70 This composition was ground to an average particle size of 1 with a sand grinder.
Shredded to the corners.

■ Preparation of dispersion B of compound (A) A dispersion liquid having the following composition was prepared by a conventional method.

l! Yutaka compound (A) 20 polyvinyl alcohol 10% solution 10 water
70 This composition was ground to an average particle size of 1 in a sand grinder.

(2) Preparation of thermosensitive coloring layer To 75 parts of the above dispersion A and 8150 parts of the dispersion, 31 parts of calcium carbonate, 20 parts of the 30% paraffin dispersion,
and 180 parts of a 10% polyvinyl alcohol aqueous solution were mixed and stirred to prepare a coating solution for a heat-sensitive coloring layer.

This coating liquid was applied onto the pigment-coated surface of the pigment undercoated paper so that the dry weight was 5.0 g/rrf and dried to form a thermosensitive coloring layer, thereby producing a thermosensitive recording paper.

The heat-sensitive recording paper obtained as described above was subjected to a super calender, and its surface was measured with a smoothness meter.
It was processed to show a smoothness of 00 to 1000 seconds. Comparative tests were conducted on the test samples thus obtained for their whiteness, sensitivity, solvent resistance of the white background area, heat resistance storage stability of the image area, and humidity resistance storage stability of the image area.

The whiteness was measured using a Hunter whiteness meter manufactured by Toyo Seiki Co., Ltd.

In addition, the solvent resistance of the white background area was evaluated based on the presence or absence of color development when ethanol was applied to the white background area of the sample using a cotton swab. Furthermore, the solvent resistance was evaluated using a yellow marker ink containing a solvent by checking whether or not color developed when the marker ink was applied to the white background of the sample.

Sensitivity was evaluated using a commercially available thermal facsimile modified for testing purposes. In other words, 1 line recording time is 10
64 lines were printed under the conditions of n+sec, scanning line density of 8×8 dots/1 ml, and applied energy of 0.45 mj/dot, and the color density immediately after printing was measured.

The higher the color density immediately after printing, the higher the sensitivity.

Furthermore, the heat-resistant storage stability of the image area was evaluated as follows. That is, an image was formed in the same manner as when evaluating the sensitivity. However, the applied energy is 0.24n+j/dot
And so. After measuring the color density immediately after printing, the color density was measured after the resulting sample was left at 60°C for 24 hours. Image storage rate at this time: The heat-resistant storage stability of the image area was expressed as follows.

The moisture resistance storage stability of the image area was evaluated as follows. An image was formed in the same manner as when evaluating the heat-resistant storage stability of the image area, and the color density immediately after printing was measured. Furthermore, 40 samples were obtained.
The color density was measured after being left for 24 hours at 90% relative humidity at 1°C. Image preservation rate at this time: The humidity resistance preservation property of the image area was expressed as follows.

The results of the above tests are shown in Table 1.

Disaster 5-I The same operation as in Example 1 was performed. However, as a block isocyanate compound, compound (B) represented by the following formula was used instead of compound (A).

Compound (B) was synthesized by the following method. That is, p
-12.9 g of chlorophenol, 18.8 g of 3,4-dichlorophenylisocyanate and 1.1 g of diazabicyclo[2,2,2)octane were dissolved in 50M1 of anhydrous toluene and heated at 110°C for 30 minutes.

After neutralization with saturated NH, (/! water), it was extracted with toluene and dried using anhydrous magnesium sulfate. The solvent was further distilled off, and the obtained crystals were purified by recrystallization from ethanol. White crystals. Melting point: 152"C .

The test results are shown in Table 1.

Disaster management - The same operations as in the main example 1 were performed. However, in the preparation of dispersion B, compound (C) of the following formula was used instead of compound (A).

Compound (C) was prepared by the following method. That is, p
12.4 g of -methoxyphenol and 18.8 g of 3,4-dichlorophenylisocyanate were dissolved in 30 g of anhydrous toluene and heated at 110°C for 2 hours.

When the mixture was allowed to cool, white crystals were precipitated. The crystals were separated by filtration, washed with toluene and hexane, and then purified by recrystallization from ethanol. White crystal. Melting point: 143°C0 Test results are shown in Table 1.

Implementation spot - Soil The same operation as in Example 1 was performed. However, in the preparation of Dispersion B, Compound CD) of the following formula: %Formula %() was used instead of Compound (A).

Compound (D) was prepared by the following method.

i.e. 4,4'-isopropylidene biphenol 22
．． 8g and 3,4-dichlorophenylisocyanate 37
．． Dissolve 6g in anhydrous toluene and dissolve 11
Heated at 0°C for 2.5 hours. When the solvent was distilled off, white crystals were precipitated. After filtering the crystals, the crystals were purified by recrystallization from a mixed solvent of ethanol, ethyl acetate, and acetonitrile. White crystal. Melting point 203°C.

The test results are shown in Table 1.

Comparison 5 - The same operation as in Example 1 above was performed. However, in the preparation of dispersion B, compound (E) of the following formula is used instead of compound (A).
) was used.

[In the above formula, tBu represents a t-butyl group. ] The test results are shown in Table 1.

Stop comparison ■ - The same operation as in main example 1 was performed. However, in the preparation of dispersion B, a compound of the following formula (F
) was used.

The test results are shown in Table 1.

The same operations as in Northern Example 5 to Main Example 1 were performed. However, in the preparation of dispersion B, the compound of the following formula @! is used instead of compound (A). I
(G) was used.

Compound (G) The test results are shown in Table 1.

North comparison ±−↓ The same operation as in Example 1 was performed. However, in the preparation of dispersion B, 4°4'-isopropylidene biphenol was used instead of compound (A).

The test results are shown in Table 1.

[Effects of the Invention] As is clear from Table 1 above, the heat-sensitive recording material of the present invention is superior to Comparative Example 4 in terms of whiteness, solvent resistance, heat-resistant storage stability, and humidity-resistant storage property. This is significantly superior to thermal recording materials using phenolic color developers.

Comparative example 1.2゜3 is the above-mentioned Japanese Patent Application Laid-open No. 60-1848.
No. 79 lists heat-sensitive recording materials using color developers as examples, but all of them have extremely low sensitivity. When compared with these, all of the heat-sensitive recording bodies shown in Examples have high sensitivity. As described above, the heat-sensitive recording material of the present invention has excellent whiteness, solvent resistance, heat-resistant storage stability, and moisture-resistant storage stability, and is also highly sensitive, making it extremely practical.

Claims (1)

[Scope of Claims] 1. A sheet-like substrate, a colorless or light-colored dye precursor formed on at least one surface of the sheet-like substrate, and a developer that reacts with the dye precursor under heating to develop color. 1. A heat-sensitive recording material, comprising: a heat-sensitive coloring layer containing a coloring agent, wherein the color developer contains a blocked isocyanate compound obtained by a reaction between 3,4-dichlorophenylisocyanate and a phenol compound. 2. The blocked isocyanate compound has the following formula (
I): ▲There are mathematical formulas, chemical formulas, tables, etc.▼The heat-sensitive recording material according to claim 1, which is a compound represented by (I).