JPH04286686A - Thermal recording material - Google Patents

Abstract

PURPOSE:To obtain a thermal recording material which is excellent in shelf life by a method wherein a thermal coloring layer containing a dye precursor and a developer is provided, and the thermal coloring layer is made to contain a compound to be expressed by a specific general formula. CONSTITUTION:A thermal recording material is obtained by providing a sheet like base material and a thermal coloring layer which is formed on at least one surface of the sheetlike base material and contains a colorless or light- colored dye precursor and a developer which reacts on the dye precursor by heating to color. The thermal coloring layer contains at least one kind of a compound to be expressed by the formula I (R1 represents a radical to be expressed by the formula II, Z represents one radical selected among NH, COO, and SO3 radicals, k represents an integer of 1-5, Y1, Y2 represent respectively one radical selected among halogen atoms, lower alkyl radical, and lower alkoxy radical independently from others, m represents 1 or 2, n represents 0 or 1, and p and q represent 0, 1, 2.). The thermal recording material shows excellent stability in shelf life concerning oil resistance or the like of a color image.

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 medium having excellent storage stability. In more detail, it has excellent storage properties such as heat resistance, moisture resistance, plasticizer resistance, oil resistance, etc., and high whiteness, and is suitable for labels such as image recording paper, facsimile paper, train tickets, commuter passes, and POS labels. ,
The present invention also relates to a heat-sensitive recording material useful for cards such as prepaid cards and pass tickets.

0002

[Prior Art] Heat-sensitive recording materials are generally made by coating a color-forming substance such as an electron-donating leuco dye, an electron-accepting phenolic compound, or an organic acid on a support such as paper, synthetic paper, or plastic film. A heat-sensitive coloring layer containing a color-developing substance as a main component is provided, and a recorded image can be obtained by causing the coloring component to react with thermal energy. Such a heat-sensitive recording medium is, for example,
4160, Special Publication No. 45-14039, and Special Publication No. 4
8-27736, etc., and has been widely put into practical use.

Since the recording device is relatively compact, inexpensive, and easy to maintain, thermosensitive recording media can be used for the output of electronic computers, facsimile machines, automatic ticket vending machines, printers for scientific measuring instruments, or CRTs for medical measurement. Widely used in printers, etc.

However, in conventional heat-sensitive recording materials in which only a heat-sensitive color-forming layer containing a color-forming dye substance, a color-developing substance, and a binder as active ingredients is coated on a support, the image after color development is It is unstable to light, water, heat, plasticizers, oil, etc., and for this reason, there is always a problem of changes in colored images over time during storage, that is, fading of colored images.

In other words, when desired printing is performed on such a conventional heat-sensitive recording medium, the recorded colored image is extremely vividly colored, but the colored image portion is exposed to water, cling film, oil, etc. etc., or high temperature (40~60℃).
℃) and high humidity (relative humidity of 60% or more) for a long time, significant discoloration occurred.

[0006] Discoloration of colored images is particularly noticeable in color-forming type thermal recording materials, that is, dye-coloring type thermal recording materials that use dye precursors mainly consisting of colorless or light-colored lactone ring compounds. In particular, there has been a strong desire to resolve this common problem that occurs when it comes into contact with plasticizers and oils.

In order to improve the storage stability, it has been proposed to add a phenolic antioxidant to the heat-sensitive coloring layer or to provide a surface layer on the heat-sensitive coloring layer. For example, JP-A-60-78782, JP-A-59-1672
No. 92, JP-A-59-114096, JP-A-59-9
As seen in various publications such as No. 3387, a phenolic antioxidant is blended into a heat-sensitive coloring layer, or as seen in JP-A-56-146796, it protects a hydrophobic polymer compound emulsion, etc. What was used for the layer,
Alternatively, as seen in JP-A-58-199189, a water-soluble polymer compound or a hydrophobic polymer compound emulsion is provided as an intermediate layer on the heat-sensitive coloring layer, and a hydrophobic polymer compound is placed thereon as a resin component. A surface layer coated with an oil-based paint has been reported.

[0008] The formulation of the above-mentioned phenolic antioxidant is as follows:
This causes background stains (decreased whiteness) in the heat-sensitive coloring layer, and in particular,
Density in non-image areas tends to increase when stored at high temperatures (60°C). In addition, the heat resistance, moisture resistance,
Plasticizer and oil resistance are also inadequate. Further, even for those in which an overcoat layer is provided on the heat-sensitive coloring layer, the storage stability under high temperature and high humidity cannot be said to be perfect. Furthermore, the heat-sensitive recording material coated with such an overcoat layer is cut,
Heat-sensitive recording materials manufactured by applying adhesive processing, etc., are susceptible to oil and other substances that penetrate through the cut surface and cause the printed area to fade.
The application of an overcoat layer had problems, such as that it could hardly be said to be an essential solution.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to solve these problems and provide a heat-sensitive recording material having excellent storage properties such as heat resistance, moisture resistance, plasticizer resistance, and oil resistance. The present invention aims to provide a heat-sensitive recording material with significantly improved plasticizer properties and oil resistance. In particular, the present invention is suitable for use in, for example, thermal recording type tickets for automatic ticket vending machines, coupon tickets and commuter passes that require long-term storage, and the use of barcode systems for POS to store fresh foods and oil types. This heat-sensitive recording material is not only suitable for label paper to be attached to the packaging surface of meats with a high content of polyvinyl chloride, but can also be used as facsimile paper for long-term storage, word processing paper, and CRT image printer paper. It is an attempt to provide the body.

0010

[Means for Solving the Problems] In the present invention, when a specific epoxy group-containing compound is added as a storage stabilizer to the heat-sensitive coloring layer together with a dye precursor, a color developer, and a binder, it is possible to The inventors have succeeded in solving the above problem by discovering that the storage stability of colored images is significantly improved even in a humid environment or under conditions in which they come into contact with plasticizers and oils and fats.

That is, the heat-sensitive recording material of the present invention comprises a sheet-like substrate, a colorless to light-colored dye precursor formed on at least one surface of the sheet-like substrate, and a dye precursor that reacts with the dye precursor under heating. It has a heat-sensitive color-forming layer containing a color developer that causes the color to develop, and the heat-sensitive color-forming layer further has a general formula (
I):

It is characterized by containing at least one compound represented by the following formula.

0012

[Function] The thermosensitive coloring layer of the thermosensitive recording material of the present invention is composed of a colorless or light-colored basic leuco dye (dye precursor), and a color developer that can develop this dye precursor and color under heating. A colored image is formed using a color reaction, and is characterized by containing at least one epoxy group-containing compound of the above general formula (I) in this heat-sensitive coloring layer. .

[0013] The reason why such compounds as mentioned above improve shelf life is not fully clear. However, basic leuco dyes (dye precursors) and the above-mentioned epoxy group-containing compounds alone do not provide sufficient print density, and the storage stability of colored images is also insufficient. It has been found that by the presence of the color developer, sufficient color density can be obtained, and at the same time, the storage stability of the color image can be dramatically improved. Due to this fact, a colorless or light-colored basic leuco dye reacts with a color developer to form a color former with an open lactone ring, and the epoxy group of the epoxy group-containing compound is added to the carboxyl group of the dye thus formed. It is presumed that this addition creates a structure in which the dye cannot return to its original closed ring form, and that this dramatically improves the storage stability of colored dye images. However, the present inventors do not insist on such a mechanism for improving storage stability.

Specific examples of the compound of general formula (I) used in the present invention include the following.

[Chemical formula 3]

In the present invention, it is essential that the epoxy group-containing compound of the general formula (I) is used together with a dye precursor and a color developer. Furthermore, a thermoplastic substance (so-called sensitizer) may also be added within a range that does not inhibit the desired effects of the present invention.

The amount of the epoxy group-containing compound of general formula (I) used is preferably 10 to 1000% by weight, more preferably 50 to 300% by weight, based on the weight of the dye precursor. When the epoxy group-containing compound of general formula (I) is contained in a proportion of less than 10% by weight,
The degree of improvement in storage stability may not be sufficient. on the other hand,
If it is present in an amount greater than 1000% by weight, the color density may be lowered, but the storage stability will not be improved and this will be economically disadvantageous.

In the present invention, the leuco dye used as a dye precursor can be selected from conventionally known ones, such as 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide ( crystal violet lactone), 3-(p-dimethylaminophenyl)
-3-(1,2-dimethylindol-3-yl)phthalide, 3-(p-dimethylaminophenyl)-3-(2
-phenylindol-3-yl)phthalide, 3,3-
Triarylmethane dyes such as bis-(9-ethylcarbazol-3-yl)-5-dimethylaminophthalide and 3,3-bis-(2-phenylindol-3-yl)-5-dimethylaminophthalide , 4,4'-bisdimethylaminobenzhydrin benzyl ether, N-halophenyl leuco auramine, N-2,4,5-trichlorophenyl leuco auramine, etc., diphenylmethane dyes, benzoyl leucomethylene blue, p-nitro Thiazine dyes such as benzoylleucomethylene blue, 3-
Spiro dyes such as methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3-benzyl-spiro-dinaphthopyran, 3-methylnaphtho(3-methoxybenzo)-spiropyran, 3-(N-ethyl-N-isopentyl) amino)-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-(
o,p-dimethylanilino)fluorane, 3-(N-ethyl-p-toluidino)-6-methyl-7-anilinofluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3- dibutylamino-6-methyl-7-anilinofluorane, 3-(N-cyclohexine-N-methylamino)-6-methyl-7-anilinofluorane,
3-diethylamino-7-(o-chloroanilino)fluoran, 3-diethylamino-7-(m-trifluoromethylanilino)fluoran, 3-diethylamino-6
-Methyl-7-chlorofluorane, 3-diethylamino-6-methylfluorane, 3-(N-ethyl-N-hexylamino)-6-methyl-7-(p-chloroanilino)fluorane and 3-cyclohexylamino- One or more types selected from fluoran dyes such as 6-chlorofluorane can be used.

The color developer used in the present invention can be selected from conventionally known phenols and organic acids. For example, bisphenol A, benzyl p-hydroxybenzoate (Japanese Patent Application Laid-open No. 140483/1983), bisphenol S
, 4-hydroxy-4'-isopropyloxydiphenyl sulfone (JP-A-60-13852), 1,1-di(4-hydroxyphenyl)cyclohexane, 1,7-
Di(4-hydroxyphenylthio)-3,5-dioxaheptane (JP-A-59-52694), 3,3'-diallyl-4,4'-dihydroxydiphenylsulfone (
One or more types selected from JP-A No. 60-208286) can be used.

The amount of color developer used in the present invention is preferably 20 to 1000% by weight, more preferably 50 to 500% by weight, based on the weight of the dye precursor. If the color developer is contained in a proportion lower than this range, the color density will be low and the storage stability of the color image will not be sufficiently improved. On the other hand, if the amount exceeds the above upper limit, the color density will decrease due to the dilution effect, but storage stability will not be improved and it will be economically disadvantageous.

The binder used in the heat-sensitive coloring layer of the present invention can be selected from those used in conventional heat-sensitive coloring layers, such as polyvinyl alcohol of various molecular weights, starch and its derivatives, methoxycellulose, etc. , cellulose derivatives such as carboxymethylcellulose, methylcellulose, and ethylcellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylic amide/acrylic ester copolymer, acryl amide/acrylic ester/methacrylic acid ternary copolymer, styrene/anhydride Water-soluble polymeric materials such as maleic acid copolymer alkali salts, polyacrylamide, sodium alginate, gelatin, and casein, as well as polyvinyl acetate, polyurethane, styrene/butadiene copolymers, polyacrylic acid, polyacrylic esters, Latexes such as vinyl chloride/vinyl acetate copolymer, polybutyl methacrylate, ethylene/vinyl acetate copolymer, and styrene/butadiene/acrylic copolymer can be used. The content of the binder in the thermosensitive coloring layer is preferably 0.5 to 40% by weight based on the weight of the thermosensitive coloring layer.

In the present invention, the heat-sensitive coloring layer contains additives such as a sensitizer, an inorganic pigment, and waxes in addition to the dye precursor, developer, binder, and specific epoxy group-containing compound. Good too. The content of these additives is preferably 90% by weight or less based on the weight of the heat-sensitive coloring layer,
More preferably, it is 20 to 70% by weight.

As the sensitizer, a thermofusible organic compound having a melting point of 50 to 150°C is used. For example, 1-hydroxy-2-naphthoic acid phenyl ester
No. 191089), p-benzylbifnyl (Japanese Patent Application Laid-open No. 1983
-82382), benzyl naphthyl ether (JP-A No. 58-87094), dibenzyl terephthalate (JP-A No. 58-98285), benzyl p-benzyloxybenzoate (JP-A No. 57-201691), diphenyl carbonate , ditrilyl carbonate (JP-A-58-136489)
, m-terphenyl (JP-A-57-89994), 1
, 2-bis(m-tolyloxy)ethane (Unexamined Japanese Patent Publication No. 1986-
56588), 1,5-bis(p-methoxyphenoxy)-3-oxapentane (JP-A-62-18118)
No. 3), oxalic acid diester (Japanese Unexamined Patent Publication No. 1583/1983), and the like.

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 clay, talc, and Examples include surface-treated 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 heat-sensitive coloring layer of the present invention may contain various waxes, if necessary. As these waxes, known waxes such as paraffin, amide wax, bisimide wax, and metal salts of higher fatty acids can be used.

The sheet-like substrate used in the heat-sensitive recording medium of the present invention can be selected from paper, coated paper whose surface is coated with pigment or latex, synthetic paper, plastic film, or a composite sheet of these. can.

To produce the heat-sensitive recording material of the present invention, a coating solution containing a mixture of the above-mentioned necessary components is applied onto at least one surface of a sheet-like substrate and dried to produce the heat-sensitive recording material. The coating amount of the coating liquid is 1 to 15% when the coating liquid layer is dry.
g/m2, preferably 2 to 10 g/m2
is particularly preferred.

If necessary, a protective layer or an undercoat layer may be provided on the thermosensitive coloring layer and/or below the thermosensitive coloring layer, or a protective layer or a conductive layer may be provided on the back surface of the sheet-like substrate.

The heat-sensitive recording material of the present invention thus obtained has a high degree of whiteness, does not cause fading in the colored recorded image area, and has excellent storage stability.

[0029]

[Examples] The present invention will be specifically explained below with reference to Examples. In addition, unless otherwise specified, "part" and "%" are
Represents "parts by weight" and "% by weight", respectively.

Example 1 A thermosensitive recording paper was prepared by the following procedure. ■ Preparation of dispersion liquid A Ingredients
amount(
part) 3-(N-isopentyl-N-ethylamino)
20 -6-Methyl-7-anilinofluorane
Polyvinyl alcohol 10% aqueous solution
10 water

70 The above composition was subjected to a sand grinder and ground until the average particle size was 1 μm.

■ Preparation of dispersion B Components
amount(
part) 4,4'-isopropylidene biphenol
10
p-benzylbiphenyl
10
Polyvinyl alcohol 10% liquid
10 water

7
0 The above composition was subjected to a sand grinder and ground until the average particle size was 1 μm.

■ Preparation of dispersion C Components
amount(
part) 4,4'-diglycidylaminobiphenyl
20 Sulfone (Compound Example (1))

Polyvinyl alcohol 10% aqueous solution
10 water

70
The above composition was subjected to a sand grinder and ground until the average particle size was 1 μm.

■ Preparation of coloring layer 40 parts of the above liquid A, 160 parts of liquid B, 40 parts of liquid C, 40 parts of calcium carbonate pigment, 20 parts of 30% paraffin dispersion,
and 120 parts of a 10% polyvinyl alcohol aqueous solution were mixed and stirred to prepare a coating solution. Apply this coating liquid with a basis weight of 50
The coating amount after drying is 7.0 g on one side of the g/m2 base paper.
/m2 and dried to form a heat-sensitive coloring layer to prepare heat-sensitive recording paper.

The heat-sensitive recording paper obtained as described above was treated with a supercalender to check the smoothness of its surface.
The time was 600 to 1000 seconds.

The thermal recording paper thus obtained was tested at a temperature of 120° C. and a pressure of 2.0° C. using a thermal gradient tester manufactured by Toyo Seiki.
When the sample was heated for 5 seconds under the condition of 5 kg/cm2 to develop color, it was found to be more than 1.1 (Macbeth reflection densitometer RD-
A clear black colored image with high density (measured by 914) was obtained.

Further, the density of the uncolored area (blank area) of the sample was measured using the above densitometer, and the measured value was expressed as the degree of whiteness. Next, a predetermined test piece was prepared from this colored sample by a conventional method, and the plasticizer resistance and oil resistance of the colored part were measured by the following test. The results are shown in Table 1.

(a) Plasticizer resistance test (PVC film resistance test): A vinyl chloride wrap film (manufactured by Mitsui Toatsu Chemical Co., Ltd.) is wrapped three times around a paper tube, and a colored image is placed on the test piece. Sandwich the specimen so that the surface is facing outward, then wrap a vinyl chloride wrap film three times over it, leave it at room temperature for 24 hours, and then measure the concentration of the specimen again using a Macbeth densitometer to determine its plasticizer resistance. was evaluated.

(b) Oil resistance test: A test piece was coated with cottonseed oil, left for 4 hours at room temperature, and then wiped off.The remaining density of the colored image was measured using a Macbeth densitometer to evaluate oil resistance. The test results are shown in Table 1.

Example 2 The same operation as in Example 1 was carried out. However, in preparing Solution C used for forming the heat-sensitive coloring layer, 3,3' diglycidylaminobiphenyl sulfone (Compound Example (2)) was used instead of 4,4'-diglycidylaminobiphenyl sulfone.
was used. The test results are shown in Table 1.

Example 3 The same operation as in Example 1 was carried out. However, in preparing Liquid C used for forming the heat-sensitive coloring layer, 4,4'-biphenylsulfone dicarboxylic acid diglycidyl ester (
Compound Example (4)) was used. The test results are shown in Table 1.

Example 4 The same operation as in Example 1 was carried out. However, in preparing Solution A used for forming the heat-sensitive coloring layer, 3-diethylamino-6-methyl was used instead of 3-(N-isopentyl-N-ethylamino)-6-methyl-7-anilinofluorane. -7-anilinofluorane was used. Table 1 test results
Shown below.

Example 5 The same operation as in Example 1 was carried out. However, 4,4'-dihydroxydiphenyl sulfone was used in place of 4,4'-isopropylidene biphenol in preparing Solution B used for forming the heat-sensitive coloring layer. The test results are shown in Table 1.

Comparative Example 1 The same operation as in Example 1 was carried out. However, liquid C was not blended in the formation of the heat-sensitive coloring layer. The test results are shown in Table 1.

Comparative Example 2 The same operation as in Example 4 was carried out. However, liquid C was not blended in the formation of the heat-sensitive coloring layer. The test results are shown in Table 1.

Comparative Example 3 The same operation as in Example 5 was carried out. However, liquid C was not blended in the formation of the heat-sensitive coloring layer. The test results are shown in Table 1.

[Table 1]

[0046] As is clear from Table 1, each of the Examples had a high degree of whiteness, and satisfactory results were obtained in each of the oil resistance and plasticizer resistance tests. However, all of the comparative examples were inferior in all of the oil resistance and plasticizer resistance tests.

[0047]

[Effects of the Invention] The heat-sensitive recording material of the present invention has excellent heat resistance, moisture resistance, oil resistance, plasticizer resistance, etc., and is particularly excellent in oil resistance and plasticizer resistance of colored images. It shows storage stability and is extremely useful in practice.

Claims (1)

[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 color developer that reacts with the dye precursor under heating to develop color. 1. A heat-sensitive recording material, comprising a heat-sensitive color forming layer comprising: a heat-sensitive color forming layer, the heat-sensitive color forming layer further containing at least one compound represented by the general formula (I): [Image Omitted]