JP2637747B2 - Thermal recording material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a heat-sensitive recording material which has excellent thermal responsiveness and little scum on a thermal head. (B) Prior art A thermosensitive recording material generally comprises a support provided with a thermosensitive recording layer mainly composed of an electron-donating, usually colorless or pale-colored dye precursor and an electron-accepting developer. By heating with a head, a hot pen, a laser beam, etc., the dye precursor and the color developer react instantaneously, and a recorded image is obtained, as reported in JP-B-43-4160 and JP-B-45-14039. It is disclosed. Such a thermosensitive recording material can be recorded with a relatively simple device. It has advantages such as easy maintenance and no noise generation, and is used in a wide range of fields such as measurement recorders, facsimile machines, printers, computer terminals, labels, and vending machines for tickets. Especially in the field of facsimile machines, the importance of the thermal method has been growing significantly, and accordingly, high-speed operation to reduce the transmission cost and energy saving to reduce the cost by reducing the size of the facsimile device are being promoted. Speed up such facsimile
Higher sensitivity of thermal recording materials has been required in response to lower energy. On the other hand, the dot density of the conventional thermal head was generally 8 dots / mm, but the dot density has been increased to 16 dots / mm, for example, and the dot area has also become smaller. The need for gradation printing by the method has increased, and it has become even more important than ever to obtain images with good printability, that is, images that faithfully reproduce the dots of the head. In order to achieve these demands, if the recording paper is strongly treated with a super calender to improve the adhesion of the recording paper to the thermal head, there will be a defect such as the so-called background fog, which reduces the whiteness. JP-A-56-27394 proposes to provide an undercoat layer between the heat-sensitive layer and the base paper, whereby a high-density image can be obtained with a small applied energy without performing a strong supercalendering process. High sensitivity has become possible. It is considered that the application of the undercoat layer is effective in smoothing the surface after the application of the heat-sensitive coating layer by forming a smoother surface by filling the unevenness of the support. As described above, the application of the undercoat layer has made the sensitivity higher than before. However, in recent years, there has been a demand for higher sensitivity and an improvement in dot reproducibility. It is no longer possible to deal with just coating the coat layer. (C) Problems to be Solved by the Invention The present invention provides a thermal paper with good thermal response in response to the demand for higher sensitivity and improved dot reproducibility, which cannot be solved by such conventional techniques. The purpose is to provide. (D) Means for Solving the Problems To summarize the constitution of the present invention, as an undercoat layer provided between the support and the heat-sensitive coating layer, a urea-formaldehyde resin is powdered in the first layer and the main component is coated with a undercoat layer of coating the two-layer structure as a main component of the pigment layer thereon as the second layer, coating amount of the pigment of the second undercoat layer is 0.8~10.0g / m ² It is characterized by In other words, the coating of the urea-formaldehyde resin powder on the first layer has the effect of forming a smoother surface by burying the irregularities of the support just like the undercoat layer coated with the pigment. The small thermal conductivity of the urea-formaldehyde resin itself and the air retention of the porous urea-formaldehyde resin powder combine to show an insulating effect.
It is thought that the heat energy from the thermal head escapes to the outside of the system, and the effect of applying the thermal energy to the thermal layer more effectively is shown. However, when the heat-sensitive layer is provided directly on the urea-formaldehyde resin powder layer, the coloring component dissolved by the thermal energy from the heat-sensitive head is sucked into the porous urea-formaldehyde resin layer, and the color-developed image is hidden. Instead, the image density decreases. For this purpose, coating a pigment layer as a second layer on the urea-formaldehyde resin powder layer prevents this and at the same time smoothes the surface smoothed by coating the first layer. It is thought that there is an action to do. As the pigment used in the second layer of the present invention, pigments usually used for coated papers and the like can be used. For example, potassium carbonate, kaolin, calcined kaolin, zinc oxide, titanium oxide,
Examples include aluminum hydroxide, zinc hydroxide, barium sulfate, and silicon oxide. Among them, pigments with an oil absorption of 70 ml / 100 g or more, especially calcined kaolin and silicon oxide, adsorb the heat-melted heat-sensitive coating layer components without the concealing effect of urea-formaldehyde resin powder, in addition to the effects described above. However, it is also a preferred pigment because it also has the effect of reducing the adhesion of debris to the hot bed. The urea-formaldehyde resin powder of the first layer in the present invention is effective if it is smeared at 1 g / m ² or more, but if it is smeared too much, it is more a paper property than a heat-sensitive property, for example, the thickness of the coating layer. If the base paper is thinned and the thickness of the smeared paper is uniform because of the increase in thickness, problems will occur in the strength of the waist, so a smearing amount of 3 to 15 g / m ² is preferable. The coating amount of the pigment in the second layer is 0.8 to 10.0 g / m ² so as not to impair the effect of the first layer and to act as the second layer. When the amount of smearing of the second layer is increased, the heat transfer is deteriorated, and the heat retaining / insulating effect of the first layer cannot be sufficiently utilized. It is preferable that the amount of the urea-formaldehyde resin powder in the first undercoat layer is larger than the amount of the pigment in the second undercoat layer.

By providing a heat-sensitive layer on the undercoat layer thus coated, desired characteristics can be obtained. The dye precursor used in 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-dimethylamino) Phenyl) phthalide, 3- (p-dimethylaminophenyl) -3- (1,2-
Dimethylindol-3-yl) phthalide, 3- (p-dimethylaminophenyl) -3- (2-methylindol-3-yl) phthalide, 3- (p-dimethylaminophenyl) -3- (2-phenylindole -3-yl) phthalide, 3,3-bis (1,2-dimethylindol-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-phenylindole-3 -Yl) -5-dimethylaminophthalide, 3-p-dimethylaminophenyl-3- (1-methylpyrrol-2-yl) -6-dimethylaminophthalide, etc. (2) Diphenylmethane compounds 4,4'- Bis-dimethylaminophenyl benzhydryl benzyl ether, N-halophenyl leuco auramine, N-2,4,5-trichlorophenyl leuco auramine and the like. (3) Xanthene compounds Rhodamine B Anilinolactam, Rhodamine Bp-
Chloroanilinolactam, 3-diethylamino-7-dibenzylaminofluoran, 3-diethylamino-7-octylaminofluoran, 3-diethylamino-7-phenylfluoran, 3-diethylamino-7-chlorofluoran, 3- Diethylamino-6-chloro-7-methylfluoran, 3-diethylamino-7- (3,4-dichloroanilino) fluoran, 3-diethylamino-7- (2-chloroanilino) fluoran, 3-diethylamino-6-methyl- 7-anilinofluoran, 3- (N-ethyl-N-tolyl) amino-6-methyl-7-anilinofluoran, 3-
Piperidino-6-methyl-7-anilinofluoran, 3-
(N-ethyl-N-tolyl) amino-6-methyl-7-
Phenethylfluoran, 3-diethylamino-7- (4-
Nitroanilinofluoran, 3-dibutylamino-6-methyl-7-anilinofluoran, 3- (N-methyl-N-
Propyl) amino-6-methyl-7-anilinofluoran, 3- (N-ethyl-N-isoamyl) amino-6-methyl-7-anilinofluoran, 3- (N-methyl-N-
Cyclohexyl) amino-6-methyl-7-anilinofluoran, 3- (N-ethyl-N-tetrahydrofuryl)
Amino-6-methyl-7-anilinofluoran and the like. (4) Thiazine compounds benzoyl leucomethylene blue, p-nitrobenzoyl leucomethylene blue and the like. (5) Spiro compound 3-methylspirodinaphthopyran, 3-ethylspirodinaphthopyran, 3,3'-dichlorospirodinaphthopyran, 3
-Benzylspirodinaphthopyran, 3-methylnaphth-
(3-methoxybenzo) spiropyran, 3-propylspirobenzopyran and the like can be mentioned, and these can be used alone or as a mixture of two or more. As the color developer used in the present invention, an electron-accepting substance generally used for thermal paper is used. In particular, a phenol derivative, an aromatic carboxylic acid derivative or its metal compound, N, N'-diarylthiourea Derivatives are used. Of these, phenol derivatives are particularly preferred, and specifically, 1,1-bis (p-hydroxyphenyl) propane, 2,2
-Bis (p-hydroxyphenyl) propane 2,2-bis (p-hydroxyphenyl) butane, 2,2-bis (p-hydroxyphenyl) hexane, bisphenolsulfone, bis (3-allyl-4-hydroxyphenyl) sulfone , 4-Hydroxy-4'-isopropyloxydiphenylsulfone, 3,4-dihydroxy-4'-methyldiphenylsulfone, diphenol ether, benzyl p-hydroxybenzoate, propyl p-hydroxybenzoate, butyl p-hydroxybenzoate And so on. Other pigments, sensitizers, antioxidants, anti-sticking agents, etc. are added to the heat-sensitive coating layer as needed. In the present invention, various adhesives that are usually used are used as a dye precursor, a color developer, other additives, and an adhesive used for a urea-formaldehyde resin used for the undercoat layer, a pigment for the second layer, and the like. be able to. For example, starches, hydroxyethylcellulose, methylcellulose, carboxymethylcellulose, gelatin, casein, polyvinyl alcohol, modified polyvinyl alcohol, sodium polyacrylate, acrylamide / acrylate copolymer acrylamide / acrylate / methacrylic acid 3 Water-soluble adhesives such as copolymers, alkali salts of styrene / maleic anhydride copolymers, alkali salts of ethylene / maleic anhydride copolymers, polyvinyl acetate, polyurethane, polyacrylate,
Latexes such as styrene / butadiene copolymer, acrylonitrile / butadiene copolymer, methyl acrylate / butadiene copolymer, ethylene / vinyl acetate copolymer and the like can be mentioned. As the support used in the present invention, paper is mainly used, but non-woven fabric, plastic film, synthetic paper, metal foil and the like or a composite sheet combining these can be used arbitrarily. (E) Embodiment Next, the present invention will be described in more detail with reference to embodiments. All parts and percentages shown below are based on weight.
The value indicating the amount of smear is the amount of smear after drying unless otherwise specified. Example 1 Preparation of Solution A (First Layer Coating Solution) A composite having the following composition was stirred to prepare a first layer coating solution. Uniseal (urea-formaldehyde resin manufactured by Ciba Geigy) 20 parts Styrene butadiene copolymer latex (50% aqueous dispersion) 6 parts Water 80 parts Preparation of solution B (coating solution for the second layer) It was prepared as a coating solution for the second layer by stirring. Ansilex (calcined kaolin manufactured by Engelhard Co.) 100 parts Styrene butadiene copolymer latex (50% aqueous dispersion) 24 parts MS4600 (Nippon Shokuhin phosphate esterified starch) (10%
Aqueous solution) 60 parts Water 52 parts Preparation of heat-sensitive coating solution Each mixture having the following composition was pulverized and dispersed in a sand mill until the average particle size became about 1 μm, and [liquid C] and [D
Liquid] was prepared. [Liquid C] 3- (N-methyl-N-cyclohexyl) amino-6-
Methyl-7-anilinofluorane 40 parts 10% polyvinyl alcohol aqueous solution 20 parts Water 40 parts [Solution D] Bisphenol A 50 parts Benzyloxynaphthalene 50 parts 10% polyvinyl alcohol aqueous solution 50 parts Water 100 parts Subsequently prepared [Solution C] Using [solution D], a heat-sensitive coating solution was prepared according to the following formulation. [Solution C] 50 parts [Solution D] 250 parts Zinc stearate (40% dispersion) 25 parts 10% aqueous solution of polyvinyl alcohol 216 parts Calcium carbonate 50 parts Water 417 parts Basis weight of each coating solution prepared in this way 40 g A thermal recording material was prepared by smearing the following amounts on a / m ² base paper with a Meyer bar. First layer 3 g / m ² Second layer 3 g / m ² Thermal layer 5.5 g / m ² Examples 2 to 4 Instead of 3 g / m ² of the first layer in Example 1, 7 g,
A heat-sensitive recording material was prepared in the same manner as in Example 1 except that 10 g and 14 g / m ² were smeared. Examples 5 to 7 In Example 1, 7 g / m ² of the first smear layer was 3 g / m ^2.
smeared m ^2, and then a heat-sensitive recording material of the second layer thereon 1 g, 6 g, except that the smear 9 g / m ² in the same manner as in Example 1. Example 8 The preparation of solution B (coating solution for the second layer) in Example 1 was carried out except that 100 parts of Ultra White-90 (coating kaolin manufactured by Engelhard Co.) was used instead of 100 parts of Ansilex. A liquid B was prepared in the same manner as in Example 1. Then, [Solution B] prepared and [Solution A] prepared in Example 1 were used.
Using a [thermosensitive coating solution], a thermosensitive recording material was prepared by smearing a base paper having a basis weight of 40 g / m ^{2 with} a Meyer bar at the following smear amount at the time of drying. First layer 7 g / m ² Second layer 3 g / m ² Thermosensitive layer 5.5 g / m ² Comparative example 1 The second layer without coating the first layer coating liquid of the coating liquid prepared in Example 1. 8 g / m ² of the coating solution was coated directly on the base paper, and 5.5 g / m ² of the thermal coating solution was coated thereon to prepare a thermal recording material for comparison. Comparative Example 2 Of the coating liquids prepared in Example 1, the coating liquid for the second layer was directly applied to the base paper at 7 g / m ² without coating the coating liquid for the first layer, and then the second layer was applied again. The coating solution was smeared at 3 g / m ² to form an undercoat layer. Next, 5.5 g / m ² of the thermosensitive coating solution was applied thereon to prepare a thermosensitive recording material for comparison. Comparative Example 3 In Example 1, the coating solution for the first layer was smeared at 7 g / m ^2, and then the heat-sensitive coating solution was smeared directly as in Example 1 without smearing the second layer to prepare a heat-sensitive recording material for comparison. did. Comparative Example 4 Each coating solution prepared in Example 1 was smeared on base paper in the following amount in the same manner as in Example 1. First layer 7 g / m ² second layer 12 g / m ² heat sensitive layer 5.5 g / m ² thus treated thermosensitive recording material was prepared in the to be 400-500 seconds Bekk smoothness supercalendered Then, the recording density, printability, and degree of adhering debris were compared using a G III fax tester. The tester used was a thermal head with a dot density of 8 dots / mm and a head resistance of 185Ω made by Okura Electric (TH-PMD), and printing was performed with a head voltage of 11 V, a conduction time of 0.5 ms and 0.8 ms. The recording density was measured with a Macbeth RD-514 reflection densitometer. Table 1 shows the results. (F) Effect As is clear from the results in Table 1, the thermal recording material of the present invention has an undercoat having a coating layer made of a urea-formaldehyde resin in the first layer and a coating layer made of the pigment in the second layer. The heat-sensitive coating layer was applied on top of the layer, and it had better thermal response than conventional heat-sensitive recording materials, and improved sensitivity and dot reproducibility without increasing the amount of head residue.

Claims (4)

(57) [Claims] A first undercoat layer is provided on a support, a second undercoat layer is provided on the first undercoat layer, and a dye precursor and the dye precursor are further heated on the second undercoat layer. In a heat-sensitive recording material provided with a heat-sensitive layer containing a color developing agent, the first undercoat layer is formed of urea-
Formaldehyde resin powder as a main component, a heat-sensitive recording the second undercoat layer mainly composed of pigment and coating amount of the pigment of the second undercoat layer is characterized by a 0.8~10.0g / m ² material. 2. The urea-formaldehyde resin powder of the first undercoat layer has a coating amount of 3 to 15 g / m ² and the urea-formaldehyde resin powder of the first undercoat layer has a coating amount of the second undercoat layer. 2. The heat-sensitive recording material according to claim 1, wherein the amount is larger than the amount of the pigment applied to the coat layer. 3. The oil absorption of the pigment in the second undercoat layer is 70%.
3. The heat-sensitive recording material according to claim 1 or 2, wherein the heat-sensitive recording material is at least ml / 100g. 4. The heat-sensitive recording material according to claim 3, wherein the pigment having an oil absorption of 70 ml / 100 g or more is calcined kaolin or silicon oxide.