JPS6153239B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to thermal recording paper, and in particular, when recording with a thermal recording device using a thermal head in which heat-generating resistive elements (dots) are lined up and fixed in a horizontal row, the thermal head and thermal recording paper are connected. This invention relates to a thermal recording paper which improves head problems such as adhesion, ie, stacking problems, and adhesion of crumbs to the thermal head, and prevents background fogging. It has been known for a long time that a colorless or light-colored color-forming substance such as crystal violet lactone reacts with a phenolic compound to form a color, and it is also possible to thermally develop a color using these substances, for example, as described in US Pat. No. 3,539,375. It is known in No. In general, in order to obtain heat-sensitive recording paper by uniformly dispersing a heat-sensitive recording composition containing a two-component color former as described above in water and coating it on a support, drying it, the two components as color formers are mixed into a water-soluble crystal. They are manufactured by separately dispersing them in an aqueous medium containing an adhesive using a ball mill or the like to form fine particles of several micrometers or smaller, and then mixing the respective dispersions, applying the mixture to a support, and drying it. In addition, particles such as various wax particles, wax emulsions, fatty acid metal salts, fatty acid amides, etc. may be contained in the heat-sensitive recording layer for the purpose of improving coloring properties, pressure coloring properties, slipperiness, etc. In order to improve the whiteness and writability of the body surface, white pigments such as clay, talc, and titanium oxide are often included. However, when thermal recording paper is manufactured, stored, or after recording, so-called background fogging may occur, causing the entire recording paper to change color and impairing its properties as a recording paper. A phenomenon in which the recording paper adheres, that is, a statesking phenomenon, may occur, impairing the feeding of the recording paper or the recording properties, or causing some of the components of the recording layer to adhere to the thermal head, or the deposits contaminating the recording paper. I had a problem. As a countermeasure against head trouble, methods have been proposed such as adding a lubricant such as a fatty acid metal salt into the recording layer, or providing a non-adhesive wax layer or a polymer film layer on the recording layer. There are problems such as insufficient effectiveness and increased manufacturing steps. In thermal recording paper, the color-forming substance and phenolic compound contained in the recording layer are heated by a thermal head.
The substances come into melting contact and a coloring reaction occurs, but at the same time, the binder and other heat-melting substances soften,
Alternatively, it may be melted, and at the stage of cooling and solidifying these softened or molten substances, it becomes adhesive to the heat head, causing a staking phenomenon. Furthermore, these molten substances turn into dust and contaminate the surface of the recording layer or the vicinity of the thermal head. The inventors of the present invention considered the causes of head troubles arising from the above-mentioned coloring principle, and as a result of studying the composition of the recording layer and the internal structure of the recording layer, the inventors found that synthetic aluminum silicate, synthetic magnesium silicate, etc. are contained inside the recording layer as a filler. It was discovered that this method was extremely effective in preventing staining and head staining, and patent applications No. 116595-1982 and 1972 were filed.
A patent application was filed on April 18th. Clay, talc, titanium oxide, etc., which are generally used in paper coatings, are sometimes added to the composition to improve the whiteness and writability of the surface of thermal recording paper, but these also prevent staining and head adhesion. However, although there is some effect, it is not sufficient. The present inventors further investigated these problems and found that hydrotalcite compounds, like synthetic aluminum silicate and synthetic magnesium silicate, are effective in preventing staking or head adhesion. That is, a hydrotalcite compound is added to the heat-sensitive recording composition in place of synthetic aluminum silicate or synthetic magnesium silicate.
It has been found that a sufficient effect is obtained when the amount is blended in an amount of up to 70% by weight, preferably 20 to 60% by weight. Furthermore, when a hydrotalcite compound was blended, it was found that it not only had an effect on staking or head adhesion, but also had an effect on preventing scalp fogging. Regarding the conventional prevention of skin fogging,
-11141 discloses a method for preventing ground coloring of heat-sensitive recording materials by adjusting the pH of the heat-sensitive coating liquid to 8 to 11.
JP-A No. 49-90142 describes a thermal paper with improved thermal stability characterized by containing calcium carbonate or magnesium carbonate in the coloring layer of the thermal recording paper, and JP-A No. 50-137147 discloses a thermal paper with improved thermal stability. , relating to a heat-sensitive recording material characterized in that it contains at least one of a polymer of N-vinyl lactams, N-vinyl cyclic carbamates, N-vinylimidazoles, or a copolymer thereof as an antifogging agent. etc. have been proposed, but the effects have not been satisfactory in any case. The mechanism of action of the hydrotalcite compound of the present invention to prevent skin fogging has not yet been elucidated, but it is thought that it is due to its strong acid adsorption ability, and the method described in the above publication It was also found that extremely good results could be obtained. Therefore, by using synthetic aluminum silicate and synthetic magnesium silicate together, it is possible to obtain even better recording paper that is free from the problems of stacking or head adhesion and is free from background fog. The hydrotalcite compounds used in the present invention are all compounds whose general formula is represented by the following formula. [M _1-x ²⁺ Mx ³⁺ (OH) ₂ ] ^x+
[Ax/n ^n-・mH ₂ O] ^x- where M ²⁺ : Divalent metal, e.g. Mg ²⁺ , Zn ²⁺ , Ni ²⁺ M ³⁺ : Trivalent metal, e.g. Al ³⁺ , Fe ³⁺ , Cr ³⁺ A ^n- : n-valent anion such as Cl ^- , NO ₃ ^- ,
CO ₃ ^2- , salicylic acid, oxalic acid, citric acid 0<x<0.33 Of these, the most commonly used are [Mg ₆ Al ₂ (OH) ₁₆ ] [CO ₃・4H ₂ O] or [Mg ₄ Al ₂ (OH) ₁₂ ] [CO ₃・3H ₂ O]. Next, the constituent materials of the thermal recording paper according to the present invention will be described. The composition of the heat-sensitive recording layer is mainly composed of a colorless or light-colored color-forming substance, a phenolic compound, and a binder. a Colorless or light-colored color-forming substance Generally called a leuco compound, it is a substance that develops color by reacting with an acidic substance, such as triphenylmethane type, triphenylmethane-phthalide type, fluoran type, leuco auramine type, spiropyran type, etc. Examples include various leuco bodies such as indoline type and indigo type. b Phenolic compound A substance that is solid at room temperature, softens or melts when heated, and develops a color when it comes into contact with the above leuco compound, such as 4,4'-isopropylidene diphenol (bisphenol A), 4 - Tertiarybutylphenol, 4-phenylphenol, 4-hydroxydiphenoxide, α-
Naphthol, β-naphthol, methyl-4-hydroxybenzoate, 4'-hydroxyacetophenone, 4-tertiaryoctylcatechol, 2,2'-dihydroxydiphenyl, 2,
2'-methylenebis(4-chlorophenol),
4,4'-Secondary butylidene diphenol,
Examples include 4,4'-isopropylidene bis(2-methylphenol) and 4,4'-isopropylidene bis(2,6 dimethylphenol). c. Binder A water-soluble binder is mainly used as the binder, and the two-component coloring agent is coated during dispersion so that no color develops when the two components are mixed. Examples of water-soluble binders include casein, polyvinyl alcohol (hereinafter abbreviated as PVA), carboxymethylcellulose, sodium alginate, methylcellulose, hydroxyethylcellulose, polyvinylpyrrolidone, and polyacrylamide. In addition, latexes such as styrene-butadiene copolymer, polyvinyl acetate, and polyacrylic acid ester can also be used in combination with these water-soluble binders. d Other additive substances The composition of the heat-sensitive recording layer may contain other additive substances,
For example, surfactants to improve coating suitability, waxes to improve recording properties, water resistance agents to improve water resistance, etc. can be added. Furthermore, as mentioned above, white pigments such as clay, talc, and titanium oxide are blended to improve the whiteness and writability of the surface of the recording medium. The present invention will be explained in detail below using examples. Example 1 (a) Production of heat-sensitive recording composition Part A 3-pyrrolidino-6-methyl-7-anilinofluorane 3 parts by weight Stearic acid amide 15 〃 Hydrotalcite 10 〃 PVA 2% aqueous solution 20 〃 Water 20 〃 B solution Bisphenol A 9 parts by weight Stearic acid amide 10 PVA 2% aqueous solution 20 Water 20 C solution PVA 15% aqueous solution 40 parts by weight After dispersing A and B separately for 4 hours in a centrifugal rotating ball mill, A A heat-sensitive recording composition (paint) was prepared by mixing the solution, B solution, and C solution. (b) Manufacture of thermal recording paper This paint was applied to 50 g/m ² of general paper so that the coated amount after drying was 8 g/m ² to obtain thermal recording paper. Example 2 (a) Production of heat-sensitive recording composition Part A 3-pyrrolidino-6-methyl-7-anilinofluorane 3 parts by weight Stearamide 15 Hydrotalcite 1 Synthetic aluminum silicate 9 PVA 2% aqueous solution 20 〃 Water 20 〃 B liquid Bisphenol A 9 parts by weight Stearic acid amide 10 〃 PVA 2% aqueous solution 20 〃 Water 20 〃 C liquid PVA 15% aqueous solution 40 parts by weight (b) Production of thermal recording paper Same as Example 1 A thermosensitive recording paper was produced. Example 3 (a) Production of heat-sensitive recording composition Part A 3-pyrrolidino-6-methyl-7-anilinofluorane 3 parts by weight Stearamide 15 Hydrotalcite 1 Clay 9 PVA 2% aqueous solution 20 Water 20 〃 B liquid Bisphenol A 9 parts by weight Stearic acid amide 10 〃 PVA 2% aqueous solution 20 〃 Water 20 〃 C liquid PVA 15% aqueous solution 40 parts by weight (b) Production of thermal recording paper Heat-sensitive in the same manner as in Example 1 Manufactured recording paper. Comparative Examples 1 to 4 For comparison with Examples, instead of hydrotalcite in Example 1, clay (natural aluminum silicate, Comparative Example 1), talc (natural magnesium silicate, Comparative Example 2), titanium oxide (Comparative Example 3) and zinc oxide (Comparative Example 4) were used in exactly the same manner as in Example 1, except that the same amounts of each were used to obtain respective thermal recording papers. The following table shows the test results for stagnation, head adhesion, and background density of these thermal recording papers.

[Table] From the results of the table, Example 1 in which the heat-sensitive recording composition containing hydrotalcite alone, hydrotalcite and synthetic aluminum silicate according to the present invention was coated
It is clear that thermal recording paper No. 2 and No. 2 have very little staking and head adhesion, and have a low background density. In addition, in the case of Example 3, in which hydrotalcite was reduced and mixed with clay, a general pigment, at a ratio of 1:9,
Since the content of hydrotalcite was small, the effect of preventing staking and head adhesion was somewhat reduced, but even in this case, good results were obtained in terms of the effect on background fogging, which was the same as in Examples 1 and 2.

Claims (1)

[Claims] 1. A thermosensitive recording paper containing a colorless or light-colored color-forming substance and a phenolic compound, characterized in that a hydrotalcite compound is contained in the recording layer of the recording paper.