JPH0339837B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal paper in which a paper support is provided with a thermosensitive layer containing a normally colorless or slightly pale dye precursor and a phenolic substance that causes the dye precursor to develop color when heated. The present invention relates to a thermal paper with improved printability, in which a thermal layer is provided on the cast surface of the glossy paper. Furthermore, the present invention relates to a thermal paper with good printability and less background fog, in which the extraction pH of the support is 6 to 9. It has been known for a long time that a dye precursor such as crystal violet lactone reacts with a phenolic substance to produce color, and the application of this reaction to thermal paper is described in, for example, Japanese Patent Publication No. 14039/1983. It has been described and is publicly known. The thermal paper of the present invention usually uses a colorless or slightly pale dye precursor and a phenolic substance.
Each of these is separately dispersed in the form of fine particles in an aqueous medium containing a binder, and the respective dispersions are mixed. A heat-sensitive coating liquid is made by adding white inorganic or organic pigments, binders, etc. as appropriate.
This coating liquid is applied to a support, dried, and then calendered to finish the surface in order to further improve the surface smoothness. Generally, when thermal paper is used in a thermal printing method such as a facsimile machine or a printer, an electric current is instantaneously applied to the thermal head to heat it, and the thermal paper is brought into contact with it to print in color. If the contact between the print head and the print head is insufficient, the color density of the print will be low, or the color will be shaded, making it difficult to read. In practice, in order to improve the adhesion between the paper and the head, the surface of the heat-sensitive layer is usually finished by passing a super calender to a Bec. smoothness level (JIS-P8119) of 200 to 1000 seconds. However, in recent high-speed printers and G-standard high-speed facsimile machines, the printing time is very short, so it has been found that even if the Beck smoothness is sufficiently high, unevenness occurs in the printing performance. The inventors of the present invention have conducted extensive studies regarding the reproducibility of printed dots (the shape of the heating resistor is directly reproduced on thermal paper) with printers and facsimile machines, and have found that the basic smoothness of the surface of the heat-sensitive layer alone is insufficient for printing. It was found that the reproducibility was not sufficient. Since the support used in thermal paper is generally paper, the thickness of each bulp fiber is related to the reproducibility of dots during printing, and in order to eliminate this effect,
It has been proposed to provide a heat-sensitive layer on an undercoated support (Japanese Unexamined Patent Publication No. 83841/1983).
However, although providing such an undercoat layer improves printing quality, it is difficult to implement because it requires two coats, which increases the cost. The present inventors investigated a method to improve dot reproducibility without undercoating, and found that
We have arrived at the present invention. The present invention uses glossy paper as a paper support to improve dot reproducibility to a satisfactory degree. Katatsuya paper is a base paper that is made using a circular wire paper machine and cast-dried using a mirror dryer such as a Yankee dryer, so that one side is extremely glossy and the other side is rough. The paper support for conventional thermal paper generally uses high-quality paper and does not use glossy paper. As a result, the smoothness of the paper support is poor, and thermal paper using this as a paper support has uncolored areas along the fiber flow during high-speed printing, and in severe cases, 2 to 4 dots with poor print reproducibility. occurs. This is mainly due to the pulp fibers of the support, and if a thick heat-sensitive layer is applied to eliminate the influence of the pulp fibers, the coloring components will not develop effectively during high-speed printing. This results in high costs. To describe the characteristics of the thermal paper using the paper support according to the present invention in more detail, since the paper support is made using a circular paper machine, the pulp fibers are also oriented in the thickness direction of the paper, making it difficult to make fourdrinier paper. Dots should not be blurred like when using a support in a machine. Since the paper support is cast-dried using a mirror dryer, the cast surface has some fibers that are keratinized and has a smooth finish. For that reason,
When applying a water-based heat-sensitive coating liquid, the smoothness of the support is less likely to return, and even without supercalender treatment, the coating is smoother than that of a paper support produced using a fourdrinier paper machine. The pressure of the super calender in post-processing can also be reduced, resulting in less pressure build-up on the surface of the thermal paper and good printing performance. The smoothness of the cast surface of the paper support was 80 to 300 seconds in terms of Beck smoothness, and the printing performance was particularly good when it was 100 seconds or more. Because the back surface of the support is not cast-dried, the back surface has large irregularities, and when printing with facsimile, there is a large frictional resistance with the platen roll, and the thermal paper runs smoothly. The Beck smoothness of the back surface is less than 50 seconds. As described in Japanese Patent Application Laid-Open No. 54-115255, the paper is smoothed by passing it between stainless steel rolls,
The smoothness of the surface on which the heat-sensitive layer is provided
When the time is set to 500 seconds or more, the Betzk smoothness of the back surface also becomes quite high, usually 350 seconds or more. When such thermal paper is used for facsimile printing, the frictional resistance against the platen roll is small and the running properties of the thermal paper are very poor. When Katatsuya paper made so that the water extraction pH is around neutral 6 to 9 is used as a paper support, the shelf life of thermal paper (texture after being left at 60℃ for 24 hours, 40℃90 %RH after being left for 24 hours) and printability, making it possible to produce ideal thermal paper. Paper with a water extraction rating of 6 to 9 is a so-called neutral paper, and can be made using a commercially available neutral sizing agent and an internally added filler such as calcium carbonate, talc, or clay. Paper with an extraction pH of less than 6 is generally made by fixing it with vanium sulfate using rosin size, but as a paper support for thermal paper, printing properties are good if the Beck smoothness is 100 seconds or more. , there is a tendency that the long-term shelf life of the scalp becomes poor. Additionally, paper with a pH of over 9 tends to cause yellowing of the paper. The characteristics of the thermal paper of the present invention have been described above, and the materials used will be further described. Typical examples of the colorless to light-colored dye precursor used in the present invention are as follows, but the invention is not limited to these typical examples. Crystal violet lactone, malachite green lactone, 3,3-bis-(paradimethylaminophenyl)-4,5,6,7-tetrachlorophthalide, benzo-β-naphthospiropyran, 3-methyl-di-β -naphthospiropyran,
1,3,3-trimethyl-6'-chloro-8'-methoxyindolylbenzospiropyran, N-phenylrhodamine lactam, 3-ethylamino-6-
Chlorofluorane, 3-morpholino-5,6-benzofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-6,7-dimethylfluorane, 3-diethylamino-7,8- Benzofluorane, 3-diethylamino-6-methoxyfluorane, 3-diethylamino-7-dibenzylaminofluorane, 3-
Diethylamino-7-anilinofluorane, 3-
Diethylamino-5,6-benzo-7-benzylaminofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3-pyrrolidino-6
-Methyl-7-anilinofluorane, 3-N-ethyl-N-tolylamino-6-methyl-7-anilinofluorane, 3-diethylamino-7-(N
-3-trifluoromethylphenyl)aminofluorane, 3-N-methyl-N-cyclohexylamino-6-methyl-7-anilinofluorane. The phenolic substance used in the present invention has the property of liquefying or vaporizing at room temperature or higher, preferably 70°C or higher and reacting with the color-forming substance to cause it to develop a color, such as 4,4-isopropylidene diphenol, 4,4'-isopropylidene bis(2-chlorophenol), 4,4'-isopropylidene bis(2-tert-butylphenol), 4,4'-
Secondary butylidene diphenol, 4,4'-
Cyclohexylidene diphenol, 4-phenylphenol, 4-hydroxydiphenoxide, methyl-4-hydroxybenzoate, phenyl-
4-hydroxybenzoate, 4-hydroxyacetophenone, salicylic acid anilide, novolac type phenolic resin, halogenated novolac type phenolic resin, α-naphthol, β-naphthol,
2,2-bis(4-hydroxyphenyl)-n-
Mention may be made of phenolic substances such as heptane, but these examples are not intended to limit the scope of the invention. Among them, phenolic substances having two or more hydroxyl groups in one molecule generally exhibit particularly excellent effects. In the present invention, a normally colorless or light-colored color-forming substance and a phenolic substance are dispersed in a binder.
Specifically, it is preferable to grind the particles to a particle size of 5μ or less. Large particles not only make the coated surface of the thermal paper rough and reduce its commercial value, but also sometimes cause pressure coloring. In addition, activators such as dispersants and antifoaming agents can be used as grinding aids if necessary, and talc can be used as a dewhitening agent or to prevent the coated material from sticking to the thermal head during thermal printing. Fillers such as clay, calcium carbonate, etc. can also be added. Additionally, a surfactant or the like may be added to improve coating properties. In addition, in order to reduce pressure coloring, which occurs when scratched, rubbed, or pressure causes stains on the scalp, waxes can be finely pulverized in the same way as color-forming substances and phenolic substances, or they can be made into an emulsion and placed in a dispersion. It is also possible to add it to. Thermofusible binders cannot be used because they stick to the heat-generating head, and highly water-soluble binders such as starch, polyvinyl alcohol, carboxymethyl cellulose, styrene-maleic acid copolymers, hydroxyethyl cellulose, and casein are generally used. Molecular agents are used. When coating, drying is performed at a relatively low temperature using a coater head such as an air knife, rubber blade, steel blade, roll, or extrusion. Furthermore, if the paper is coated only, the surface smoothness is poor, the adhesion to the heating head is poor, and the thermal conductivity is poor, so it cannot exhibit sufficient performance as a thermal paper. Smoothing treatment can also be carried out by methods such as , gloss calendering, brushing, etc. Next, in order to specifically explain the present invention, examples will be described and explained. Example 1 A wood pulp (LBKP 80% NBKP 20%) slurry beaten to a beating degree of 63°SR was internally added with rosin size at 1.2% based on the pulp and talc at 5% based on the pulp, and then an aqueous solution of vanium sulfate was added to make the pulp. The pH of the slurry was adjusted to 5.6, and paper was made using a circular mesh paper machine.
Weigh by drying with Yankee dryer
A 52 g/m ² acidic monochrome paper was obtained. The base smoothness of the cast surface of this acidic monochrome paper is 154 seconds, and the water extraction pH is
It was 5.7. The Beck smoothness of the back surface was 13 seconds. Comparative Example 1 and Comparative Example 2 The final pulp slurry prepared in Example 1 was made into paper using a Fourdrinier paper machine, and dried using a multi-tube dryer to a weight of 52
g/m ² of acidic high-quality paper was obtained. This acidic high-quality paper
The surface smoothness is 52 seconds, and the water extraction pH is 5.7.
It was hot. (Comparative Example 1). This paper was then finished using a super calender to achieve a smoothness of 150 seconds on the front surface. (Comparative Example 2). Example 2 Light calcium carbonate (trade name: Calcium Carbonate PC, manufactured by Shiraishi Kogyo) was added internally to a slurry of wood pulp (LBKP 80%, NBKP 20%) beaten to a degree of beating of 63°SR, and 10% of the pulp was added, and a sizing agent was added. As a fixing agent for the sizing agent, cationic starch (CATO-F, manufactured by National Starch) was added at 0.3% to the pulp and 0.6% to the pulp. The paper was made into a paper using a Yankee dryer and dried using a Yankee dryer to obtain a neutral glossy paper with a basis weight of 52 g/m ² . The base smoothness of the cast surface of this neutral gloss paper is 130 seconds,
The water extraction pH was 8.2. The Beck smoothness of the back surface was 16 seconds. Comparative Example 3, Comparative Example 4 The final pulp slurry prepared in Example 2 was made into paper using a Fourdrinier paper machine, dried using a multi-tube dryer, and weighed.
A neutral high-quality paper of 52 g/m ² was obtained. The surface smoothness of this neutral high-quality paper is 54 seconds, and the water extraction pH is 8.2.
It was hot. (Comparative Example 3). Furthermore, the paper of Comparative Example 3 was produced using a supercalender with a Beck smoothness of 150 seconds. (Comparative Example 4). Comparative Example 5 The paper obtained in Comparative Example 3 was passed between stainless steel rolls to check the smoothness of the side on which the heat-sensitive layer was to be provided.
Adjusted to 500 seconds. The Beck smoothness of the back surface of this paper was 380 seconds. Preparation of thermal paper A Liquid calcium carbonate PC 7 parts by weight Sodium polyacrylate 0.05 〃 Water 7 〃 B Liquid stearamide 1 part by weight 5% hydroxyethyl cellulose 5 〃 C Liquid 4,4'-isopropylidene diphenol
1 part by weight 5% hydroxyethyl cellulose 5 D Solution 3-N-methyl-N-cyclohexylamino-
6-Methyl-7-anilinofluorane 1 part by weight 5% hydroxyethyl cellulose 5 Solution A was dispersed using a high-speed stirrer. Next, B, C,
Disperse D solution in a ball mill for 48 hours to obtain A:B:
A heat-sensitive coating liquid was prepared by mixing C:D in a weight ratio of 1:5:5:3. This heat-sensitive coating liquid was applied to the paper supports of Examples 1 and 2 and Comparative Examples 1 to 5 using an air knife coater so that the coating amount after drying was 7 g/ ^m2 , and the temperature was maintained at not higher than 60°C. Dry. (Examples 1 and 2 were coated on the cast side of glossy paper, and Comparative Examples 1 to 5 were coated on the front side of general high-quality paper.)
Furthermore, it was finished using a super calendar to achieve a Beck smoothness of 400 seconds. These thermal papers were tested using a facsimile tester manufactured by Matsushita Electronic Components at a voltage of 1.6V and a pulse width of 1.0ms.
Printing varies up to 3.3 ms, printing density, dot reproducibility, and shelf life of the background (texture change after storage at 60℃ for 24 hours...referred to as heat resistant shelf life), and 40℃, 90%
Table 1 shows the results of examining the RH, skin change after 24 hours (referred to as humidity and heat storage stability). The thermal paper of Examples 1 and 2 and Comparative Examples 1 to 4 had a large frictional resistance with the platen roll during facsimile printing, and the thermal paper ran smoothly, but the paper of Comparative Example 5 The frictional resistance with the roll was small, and the running properties of the thermal paper were very poor, making it unusable for practical use. 【table】

Claims (1)

[Scope of Claims] 1. A thermal paper in which a heat-sensitive layer mainly consisting of a combination of a colorless or light-colored dye precursor and a phenolic substance is provided on a paper support, wherein the heat-sensitive layer is made on a circular wire paper machine and is made on one side. Only the cast is provided on the cast surface of dry single-sided paper, and the base smoothness of the cast surface is 100 to 300 seconds, and the base smoothness of the opposite side of the single-sided glossy paper is 50 seconds. A thermal paper with improved printability characterized by the following: 2. The thermal paper according to claim 1, wherein the paper support has a water-extracted pH of 6 to 9.