JPH0477673B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field] The present invention relates to a heat-sensitive recording material that utilizes a color-forming reaction between a leuco dye and a color developer. It has been known for a long time that color-forming leuco dyes, which are normally colorless or light-colored, and color developers such as organic acidic substances melt and react when heated, producing color.This color-forming reaction was applied to recording paper. For example,
It is disclosed in Japanese Patent Publication No. 4160, Japanese Patent Publication No. 45-14039, etc., and is well known. These thermal recording sheets are used in a wide range of fields, including measurement recorders, terminal printers for computers, facsimile machines, automatic ticket vending machines, and barcode labels.Recently, these recording devices have become more diversified and more sophisticated. As the demand for heat-sensitive recording sheets increases, the quality required for heat-sensitive recording sheets also becomes higher. For example, with the increase in speed of thermal heads, it is now possible to record clear images with high density even with thermal energy.
There is a demand for a heat-sensitive recording sheet that has good head matching properties such as head dregs. The heat-sensitive recording sheet is colored using chromogenic leuco dye,
Both or one of the color developers melts and reacts with the thermal energy supplied from the thermal head, but one way to improve color development sensitivity is to use leuco dyes and color developers instead of leuco dyes and color developers. A method of adding a compound (generally called a thermofusible substance) that melts at a low temperature and has a high ability to dissolve both is widely known, and various compounds are disclosed in the following publications. For example, JP-A-49-34842 discloses nitrogen-containing compounds such as acetamide, stearamide, m-nitroaniline, dinitrile phthalate, etc., JP-A-52-106746 discloses acetoacetanilide, JP-A-53-39139 In the publication, alkylated biphenyl alkanes and the like are disclosed. However, in recent years, speeds have increased particularly in the field of thermal facsimile, and it has become common to drive thermal heads at high speeds, which can cause the background of heat-sensitive recording sheets to develop color during continuous recording due to heat accumulation around the head. (residual heat color development) etc. are inconvenient, so it is a challenge to increase the dynamic color development sensitivity without lowering the color development start temperature. However, although these compounds improve the static coloring sensitivity, sufficient dynamic coloring sensitivity cannot be obtained unless they are added in large quantities to the thermosensitive coloring layer. ), sticting occurs, or the melting point is too low, the storage stability (fogging on the background) of the heat-sensitive recording sheet may be reduced, making it impossible to obtain fully satisfactory results. In addition, one way to improve dynamic coloring sensitivity is to improve the surface smoothness of the thermosensitive coloring layer, or to reduce the content of components that do not participate in the coloring reaction, such as fillers and binders, in the coloring layer. However, there is also a method of increasing the coloring component density. Improving the surface smoothness can be easily achieved by calendering using a super calender, etc., but this may cause the background to develop color or increase the surface gloss, making the appearance unsuitable for recording paper. Hanama is damaged. In addition, the heat-sensitive coloring layer usually contains calcium carbonate, clay, and urea to preserve the whiteness of the background, prevent dirt from adhering to the head, and prevent staining.
Adding fillers such as formalin resin fine particles,
Water-soluble binders are added to fix the coloring components and their additives to the support, but reducing their content will not only lead to deterioration of their quality, but also cause inconvenience. Such methods also do not provide fully satisfactory results. [Objective] The object of the present invention is to provide a heat-sensitive recording material with high dynamic color density that can record clear images with high density even with minute thermal energy without impairing other properties such as staking or head matching properties. It's about doing. [Structure] That is, according to the present invention, a foam layer formed by heating and foaming a foamable plastic filler, an undercoat layer containing a filler and a binder, and a leuco dye and a color developer are formed on a support. Provided is a heat-sensitive recording material characterized in that heat-sensitive coloring layers containing the above-mentioned heat-sensitive coloring layers are provided in that order. In the present invention, a foamed layer formed by heating and foaming a foamable plastic filler is provided on a support, and a layer containing a filler and a binder is provided thereon as an undercoat layer for the thermosensitive coloring layer. , on which a heat-sensitive coloring layer containing a leuco dye and a color developer is provided, but in this case, the foam layer acts as a heat insulating layer, and the undercoat layer plays the role of evening out unevenness on the surface of the foam layer. As a result, by using both layers in combination, the heat energy from the thermal head can be effectively absorbed by the thermosensitive coloring layer.
As a result, a product with improved thermal sensitivity can be obtained. The expandable plastic filler used in the present invention is a hollow plastic filler having a shell made of thermoplastic resin and containing a low boiling point solvent and a blowing agent inside, and foams when heated. Such expandable plastic fillers are conventionally known,
Various types can be applied, but the particle diameter in an unfoamed state is 2 to 50 μm, preferably 5 to 20 μm, and in a foamed state, it is 10 to 100 μm.
m, preferably 10 to 50 μm. The thermoplastic resin that forms the shell of this plastic filler is
Examples include polystyrene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyacrylic ester, polyacrylonitrile, polybutadiene, or copolymers thereof. The blowing agent contained in the shell is generally propane, butane, etc. To form a foam layer on a support, the above-described foamable plastic filler is coated and dried on the support together with a binder, and then a hot plate is brought into close contact with the coated surface to heat and foam the plastic filler. That's fine. The amount of plastic filler applied is 1
^m2 , as unfoamed filler, at least 1
g, preferably about 2 to 5 g. Further, the amount of the binder used may be such as to strongly bond the foamed layer to the support, and is usually 5 to 50% by weight based on the total amount of the unfoamed filler and the binder. Further, the heating and foaming temperature is a temperature at which the thermoplastic resin constituting the filler shell is softened. The expansion ratio is usually 2 to 4 times, preferably about 2 to 3 times, and is appropriately selected. Since the surface of the foamed layer formed on the support as described above is considerably uneven, in the present invention, an undercoat layer containing a filler and a binder as main components is applied to the surface. will be established. This undercoat layer has a filler coating amount of 2.0
The binder content in the undercoat ^layer is preferably about 5 ^to 50% by weight. Examples of the filler to be contained in the undercoat layer include various organic or inorganic fine powders shown below in connection with the components of the heat-sensitive coloring layer. Examples include the various types shown in relation to the components. The leuco dye used in the present invention may be used alone or in combination.
The leuco dyes can be applied in a mixture of more than one species, and any of the leuco dyes that have been applied to this type of heat-sensitive material can be used, such as triphenylmethane, fluoran, phenothiazine, auramine, etc. Leuco compounds of spiropyran-based dyes are preferably used. Specific examples of such leuco dyes include those shown below. 3,3-bis(p-dimethylaminophenyl)
-phthalide, 3,3-bis(p-dimethylaminophenyl)
-6-dimethylaminophthalide (also known as crystal violet lactone), 3,3-bis(p-dimethylaminophenyl)
-6-diethylaminophthalide, 3,3-bis(p-dimethylaminophenyl)
-6-chlorphthalide, 3,3-bis(p-dimethylaminophenyl)
Phthalide, 3-cyclohexylamino-6-chlorofluoran, 3-dimethylamino-5,7-dimethylfluoran, 3-dimethylamino-7-chlorofluoran, 3-dimethylamino-7-methylfluoran, 3- Dimethylamino-7,8-benzfluorane, 3-dimethylamino-6-methyl-7-chlorofluorane, 3-(N-p-tolyl-N-ethylamino)-6
-Methyl-7-anilinofluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 2-{N-(3'-trifluoromethylphenyl)
amino}-6-diethylaminofluorane, 2-{3,6-bis(diethylamino)-9-
(o-chloroanilino)xantylbenzoic acid lactam}, 3-diethylamino-6-methyl-7-(m-
trichloromethylanilino)fluoran, 3-diethylamino-7-(o-chloroanilino)fluoran, 3-dibutylamino-7-(o-chloroanilino)fluoran, 3-N-methyl-N-amylamino-6-methyl-7- Anilinofluorane, 3-N-methyl-N-cyclohexylamino-
6-Methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-(N,N-diethylamino)-5-methyl-
3 -(2'-Hydroxy-4'-dimethylaminophenyl)-3-(2'-methoxy-5'-chlorophenyl)phthalide, 3-(2'-hydroxy-4'-dimethylaminophenyl)-3- (2'-Methoxy-5'-nitrophenyl)phthalide, 3-(2'-hydroxy-4'-diethylaminophenyl)-3-(2'-methoxy-5'-methylphenyl)phthalide, 3-(2'- Methoxy-4'-dimethylaminophenyl)-3-(2'-hydroxy-4'-chloro-5'-
methylphenyl)phthalide, 3-morpholino-7-(N-propyl-trifluoromethylanilino)fluorane, 3-pyrrolidino-7-trifluoromethylanilinofluorane, 3-diethylamino-5-chloro-7-(N-
benzyl-trifluoromethylanilino)fluorane, 3-pyrrolidino-7-(di-p-chlorophenyl)methylaminofluorane, 3-diethylamino-5-chloro-7-(α-
phenylethylamino)fluoran, 3-(N-ethyl-p-toluidino)-7-(α
-phenylethylamino)fluoran, 3-diethylamino-7-(o-methoxycarbonylphenylamino)fluoran, 3-diethylamino-5-methyl-7-(α-
phenylethylamino)fluoran, 3-diethylamino-7-piperidinofluorane, 2-chloro-3-(N-methyltoluidino)-7
-(p-n-butylanilino)fluoran, 3-(N-benzyl-cyclohexylamino)-
5,6-benzo-7-α-naphthylamino-4'-
Bromofluorane, 3-diethylamino-6-methyl-7-mesitidino-4',5'-benzofluorane, etc. Further, as the color developer used in the present invention, various electron-accepting substances that react with the leuco dye and develop color when heated are used, and specific examples thereof include phenols as shown below. Examples include acidic substances, organic or inorganic acidic substances, and salts thereof. Gallic acid, salicylic acid, 3-isopropylsalicylic acid, 3-cyclohexylsalicylic acid, 3,5
-di-tert-butylsalicylic acid, 3,5-di-α
-Methylbenzylsalicylic acid, 4,4'-isopropylidene diphenol, 4,4'-isopropylidene bis(2-chlorophenol), 4,4'-isopropylidene bis(2,6-dibromophenol), 4,4 '-isopropylidene bis(2,6-
dichlorophenol), 4,4'-isopropylidene bis(-2-methylphenol), 4,4'-isopropylidene bis(2,6-dimethylphenol), 4,4'-isopropylidene bis(2-tert-
butylphenol), 4,4'-sec-butylidene diphenol, 4,4'-cyclohexylidene bisphenol, 4,4'-cyclohexylidene bis(2
-methylphenol), 4-tert-butylphenol, 4-phenylphenol, 4-hydroxydiphenoxide, α-naphthol, β-naphthol, 3,5-xylenol, thymol, methyl-
4-hydroxybenzoate, 4-hydroxyacetophenone, novolak type phenolic resin,
2,2'-thiobis(4,6-dichlorophenol), catechol, resorcinol, hydroquinone,
Pyrogallol, phloroglycin, phloroglycin carboxylic acid, 4-tert-octylcatechol,
2,2'-methylenebis(4-chlorophenol),
2,2'-methylenebis(4-methyl-6-tert-
butylphenol), 2,2'-dihydroxydiphenyl, ethyl p-hydroxybenzoate, propyl p-hydroxybenzoate, butyl p-hydroxybenzoate, benzyl p-hydroxybenzoate,
p-chlorobenzyl p-hydroxybenzoate,
o-chlorobenzyl p-hydroxybenzoate,
p-methylbenzyl p-hydroxybenzoate,
n-octyl p-hydroxybenzoate, benzoic acid, zinc salicylate, 1-hydroxy-2-naphthoic acid, 2-hydroxy-6-naphthoic acid, 2-
Zinc hydroxy-6-naphthoate, 4-hydroxydiphenylsulfone, 4-hydroxy-4'-chlorodiphenylsulfone, bis(4-hydroxyphenyl)sulfide, 2-hydroxy-p-toluic acid, 3,5- tin di-t-butylsalicylate, tartaric acid, oxalic acid, maleic acid, citric acid, succinic acid, stearic acid, 4-hydroxyphthalic acid,
Boric acid etc. In the present invention, in order to bind and support the leuco dye and color developer on the support, various commonly used binders can be used as appropriate, such as polyvinyl alcohol, starch and its derivatives, methoxycellulose, hydroxyl, etc. Cellulose derivatives such as ethyl cellulose, carboxymethyl cellulose, methyl cellulose, ethyl cellulose,
Sodium polyacrylate, polyvinylpyrrolidone,
Acrylic amide/acrylic ester copolymer, acrylic amide/acrylic ester/methacrylic acid ternary copolymer, styrene/maleic anhydride copolymer alkali salt, isobutylene/maleic anhydride copolymer alkali salt, poly In addition to water-soluble polymers such as acrylamide, sodium alginate, gelatin, and casein, polyvinyl acetate, polyurethane, styrene/butadiene copolymer, polyacrylic acid, polyacrylic acid ester, vinyl chloride/vinyl acetate copolymer, and butyl methacrylate,
Latexes such as ethylene/vinyl acetate copolymers and styrene/butadiene/acrylic copolymers can be used. In addition, in the present invention, in addition to the leuco dye and color developer, if necessary, auxiliary additive components commonly used in this type of heat-sensitive recording material, such as fillers, surfactants, thermofusible substances ( or lubricant) etc. can be used in combination. In this case, the filler is
For example, inorganic fine powders such as calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, clay, talc, and surface-treated calcium and silica, as well as urea-
Organic fine powders such as formalin resin, styrene/methacrylic acid copolymer, and polystyrene resin can be mentioned, and examples of thermofusible substances include, for example,
In addition to higher fatty acids or their esters, amides or metal salts, various waxes, condensates of aromatic carboxylic acids and amines, benzoic acid phenyl esters,
Examples include higher linear glycols, dialkyl 3,4-epoxy-hexahydrophthalates, higher ketones, and other heat-fusible organic compounds having a melting point of about 50 to 200°C. The heat-sensitive recording material of the present invention can be produced, for example, by applying a heat-sensitive layer-forming coating solution containing each of the above-mentioned components onto a suitable support such as paper, synthetic paper, or plastic film, and drying it. Ru. [Effects] By having the above structure, the heat-sensitive recording material of the present invention can utilize the heat energy from the thermal head at a high rate for the melting reaction of the heat-sensitive coloring layer, and as a result, the heat of the product is reduced. Sensitivity is improved. [Examples] Next, the present invention will be explained in more detail by Examples and Comparative Examples. All parts and percentages shown below are based on weight. Example A foamed layer coating solution was prepared by stirring and dispersing a mixture consisting of the following formulation using a disper. Expandable plastic filler (shell: copolymer of vinylidene and acrylonitrile, blowing agent: isobutane) 15 parts 10 polyvinyl alcohol 30〃 Water 55〃 Dry and adhere the above foam layer coating solution in an unfoamed state to the surface of commercially available high-quality paper. The coating was applied to an amount of 2.0 to 3.0 g/m ² and dried, and then the coated surface was brought into close contact with the surface of a rotary drum dryer equipped with a heater, and the surface temperature was 120 to 130°C. The mixture was heated and foamed for a minute. On the other hand, a mixture having the following formulation was stirred with an agitator to prepare an undercoat layer coating solution. 40% dispersion of polystyrene resin 52.5 parts 20% starch aqueous solution 17.5〃 Styrene-butadiene latex (solid content concentration 47
%) 7.3〃 Water 22.7〃 The above-mentioned undercoat layer coating liquid was applied and dried on the foamed layer so that the dry adhesion amount was 4.0 to 5.0 g/m ² . Separately from the above, liquids [A] and [B] were prepared by pulverizing and dispersing the following mixtures using a ball mill and an attritor until the volume average particle diameter was approximately 1.5 μm. [A] Liquid composition 3-(N-cyclohexyl-N-methyl)amino-6-methyl-7-anilinofluorane 20 parts 10 polyvinyl alcohol aqueous solution 16〃 Water 64〃 [B] Liquid composition P-Benzyl oxybenzoate 20 parts Calcium carbonate 10〃 10% polyvinyl alcohol aqueous solution 30〃 Water 40〃 Both layers were mixed and stirred in water at a weight ratio of [A] solution: [B] solution = 1:4 to obtain a heat-sensitive coloring layer coating solution. Ta. This heat-sensitive coloring layer coating solution is coated on the support provided with the foamed layer and undercoat layer so that the dry adhesion amount is 3.0 to 3.0.
After coating and drying to a coating density of 4.0 g/m ² , calendering is performed using a supercalender so that the gloss level (measured in accordance with JIS-P-8142) is 10 to 13%. I got a record sheet. Comparative Example 1 A heat-sensitive recording sheet of a comparative example was obtained in the same manner as in the example except that the foam layer and under layer of the example were not provided. Comparative Example 2 A heat-sensitive recording sheet of Comparative Example 2 was prepared in the same manner as in Example except that the under layer was not provided. Each of the heat-sensitive recording sheets obtained as described above was tested for dynamic color development sensitivity using a G-FAX test machine. The results are shown in Table-1. The test machine has an 8 dot/mm thermal head manufactured by Matsushita Electronic Components Co., Ltd., and the heating resistor is approximately
400 Ω/dot, which is equivalent to a main scanning recording speed of 20
ms/line, sub-scan 3.85/mm, platen pressure 1.4
kg, head input 0.45w/dot condition, energizing time
Tests were conducted under three conditions: 1.8 msec, 1.4 msec, and 1.2 msec. In addition, states king property,
Tested with 1.8msec all solids. Temperature is measured using Macbeth densitometer (RD-514, filter wratten-106)
The concentration was measured.

[Table] As can be seen from Table 1 above, the heat-sensitive recording material of the present invention provides high color density with extremely small thermal energy. Further, there was no staking in the image, and it was confirmed that the image had extremely good staking properties.

Claims (1)

[Claims] 1. A foam layer formed by heating and foaming an expandable plastic filler, an undercoat layer containing a filler and a binder, and a heat-sensitive coloring layer containing a leuco dye and a color developer were provided in this order on a support. A heat-sensitive recording material characterized by: