JPH0326150B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a pressure-sensitive recording sheet,
More specifically, as a color developer, acid clay is treated with acid to almost completely remove aluminum ions, the aromatic adsorption index is set to 40 or more, and then a substantial amount of magnesium ions are introduced as a silica/magnesia solid acid color developer. This invention relates to improving the storage stability of colored images of pressure-sensitive recording sheets used. Pressure-sensitive recording sheets generally contain an electron-donating organic coloring agent (hereinafter referred to as coloring agent) such as crystal violet lactone or benzoyl leucomethylene blue, and a montmorillonite clay mineral (hereinafter referred to as ``coloring agent'') whose activity has been increased by acid treatment. It applies the principle of color development through the reaction of electron-accepting color developers (hereinafter referred to as color developers) such as activated clay), phenolic compounds, aromatic carboxylic acids, or metal salts thereof, and contains color formers. The top paper with the microcapsules coated on one side of the base paper and the inner paper with the microcapsules and color developer coated on different sides of the same base paper are combined as appropriate according to the purpose of use, and pressure is applied with a ballpoint pen, typewriter, etc. Then you can make a copy. There is also a type of paper called self-contained paper in which the microcapsules and color developer are coated on the same side of a base paper. In the pressure-sensitive recording sheet, activated clay is most commonly used as a color developer. This activated clay reacts well with the coloring agent and has the property of producing deep colors, but the color developing ability decreases over time, and the coloring image does not change due to nitrogen oxides etc. when left alone. It has the disadvantage of fading due to That is, the acid strength of activated clay is too strong for crystal violet lactone, which is the most commonly used coloring agent, to react with activated clay to produce the highest concentration of blue-violet color. For this reason, a method has been proposed in which an alkaline substance is added to the activated clay paint to make it slightly alkaline. but,
Over time, the alkali recrystallizes or is neutralized by sulfuric acid bands in the base paper, and its effectiveness is often lost. In addition, when amines are added, they not only neutralize the acid points in the strong acid part of the activated clay, but also neutralize the acid points in the weak acid part that contribute to the color development reaction, thereby increasing the visibility of the activated clay. There is a problem of deterioration of color function. The drawback of such a color developing sheet is that after acid clay is further acid-treated to almost completely remove aluminum ions and the aromatic adsorption index is set to 40 or more, silica-magnesia solid acid (hereinafter simply silica) into which a substantial amount of magnesium ions is introduced is used.・The decline in color developing ability over time can be improved to some extent by using magnesia (referred to as magnesia) as a color developer, but the color image is not sufficiently durable against fading due to nitrogen oxides or photofading when left alone. As a result of various studies, a significant improvement was found by using silica/magnesia and a hydroxybenzoic acid ester compound as a color developer, leading to the completion of the present invention. The silica and magnesia used in the present invention require a process of acid treatment of montmorillonite clay minerals, and montmorillonite clay minerals have the general ^formula
(Y ²⁺ , Y ³⁺ ) _2~3 N ₄ O ₁₀ (HO) ₂・SH ₂ O where X: K, Na, Ca Y ²⁺ : Mg ²⁺ , Fe ²⁺ , Mn ²⁺ , Ni ²⁺ , Zn ²⁺ Y ³⁺ : Ai ³⁺ , Fe ³⁺ , Cr ³⁺ , Mn ³⁺ Z : Si, Al The average value of m is 1/3 S is indicated by the number of interlayer water. This is described on page 80 of the Clay Handbook (edited by the Clay Society of Japan, Gihodo).
Among these clay minerals, Si100 is the acid clay.
It is preferable that the Al content is 5 to 30 parts by weight. When montmorillonite clay minerals are treated with sulfuric acid or hydrochloric acid, Fe ions, Mg ions, Ca
Ions are eluted. Next, Al ions are eluted, and the silica/magnesia used in the present invention is one that has been treated until the Al ions are substantially completely removed. At this time, the aromatic adsorption index of the treated clay must exceed 40. Here, the aromatic adsorption index is an index that reflects the degree of adsorption capacity or activity of the treated clay, and is also conveniently used as an index indicating the degree of specific surface area of the treated clay. An aromatic adsorption index of 40 or more means that the aromatic adsorption index of activated clay used as a color developer other than the present invention is 20.
~40, it is very active;
This means that the specific surface area is very large, and it also indicates that there are many acid sites in the weak acid part that contribute to color development with crystal violet lactone. It also shows that the influence of acid strength exerted by sulfate bands in the base paper over time is less likely to occur. The aromatic adsorption index is determined by the following method. Dry the pulverized sample at 150°C ± 5deg. for 3 hours and let it cool to room temperature in a desiccator. Take 1.00 g of this dried sample into a container, add 2.00 ml of a mixed solution of 30 volumes of dehydrated toluene and 70 volumes of dehydrated isooctane to disperse the sample, shake at room temperature for 40 minutes, and then precipitate the sample in a centrifuge. Collect clear liquid. The refractive index of this supernatant liquid and the original liquid was measured at 20°C,
Calculate the aromatic adsorption index (AAI) using the following formula. AAI = [(n ²⁰ _D ) A - (n ²⁰ _D ) B] × 10 ⁴ where (n ²⁰ _D ) A: Refractive index of a mixture of 30 volumes of toluene and 70 volumes of isooctane (n ²⁰ _D ) B:
Refractive index of supernatant liquid When the aromatic adsorption index of natural clays was determined using the method described above, most of them were distributed between 4 and 15.
In the case of montmorillonite type clay mineral, which is the source of activated clay, it is distributed between 8 and 15. By acid-treating this montmorillonite clay mineral, it is possible to increase the aromatic adsorption index. The treated clay from which Al ions have been removed consists only of SiO ₂ , and there are almost no acid points in the strong acid part and only acid points in the weak acid part. However, under this condition, it is difficult to develop and maintain the highest concentration of crystal violet lactone. The reason for this is thought to be that although the color-forming reaction is sufficiently carried out at an acid site weaker than the optimum acid strength for coloring crystal violet lactone at its highest concentration, on the other hand, the decomposition of the color-forming body is accelerated by light such as sunlight. Here, the acid strength can be expressed by the acidity of the treated clay, that is, the number of acid spots that have a certain strength of acid strength.
The acid sites with acid strengths suitable for color development of crystal violet lactone range from acid strength Ho=+0.8 to Ho=+4.8.
0.4 mmol/g or more is required. Therefore, the silica and magnesia used in the present invention are
By reintroducing only Mg ions into the SiO ₂ molecular structure of treated clay from which Fe, Ca, Mg, and Al ions have been removed, the acid strength ranges from Ho=+0.8 to Ho=+4.8 by 0.4 mmol/ At this time, from Ho = +0.8, there are no acid sites at all in the strong acid part, and from Ho = +4.8, the acid sites in the weak acid part are 0.4 mmol/g or less, and Crystal Bio It has the optimum acid strength for coloring rettolactone. Magnesium nitrate, magnesium chloride, magnesium perchlorate, magnesium formate, magnesium sulfate, magnesium hydroxide, magnesium carbonate, magnesium oxide, etc. are used as the Mg ⁺⁺ introduced into the treated clay made of SiO ₂ . As for the amount added
5 to 50 parts by weight of Mg per 100 parts by weight of Si, preferably
It may be introduced in an amount of 10 to 30 parts by weight. the above
Activated clay from which Al ions have been removed is added to a solution containing dissolved Mg salts and heat-treated. Alkalize and heat at 30-60℃ to fix Mg ions. Then wash with water. At this time, a short-time treatment with a weak acid such as phosphoric acid may be performed, and the silica/magnesia used in the present invention is obtained by drying at 100 to 350°C. However, this manufacturing method can be modified in many ways. As described above, the silica-magnesia solid acid, which is one of the color developers used in the present invention, is made by lightly or moderately acid-treating conventionally known activated clay, that is, natural acid clay or acid clay. It is a completely different substance (in which large amounts of naturally occurring metal cations such as magnesium, calcium, aluminum, and iron still remain); it is a synthetic solid acid, and the concept is different from activated clay. It is something to do. That is, it is a synthetic silica-magnesia solid acid. The hydroxybenzoic acid ester compound used in combination with silica/magnesia of the present invention to improve the stability of colored images is represented by the following general formula. General formula: (However, R represents an alkyl group, an aralkyl group, or an allyl group, and -COOR is at the ortho or para position with respect to -OH). The amount of these hydroxybenzoic acid ester compounds added is 5 to 100 parts by weight per 100 parts by weight of the silica-magnesia compound, and if it is less than 5 parts by weight, there is almost no effect, and if it is more than 100 parts by weight, the coloring property will be deteriorated. It can be added as is as a fine powder that has passed through a 325 mesh fluid, but from the viewpoint of color development and surface smoothness, a small amount of dispersion aid is used and a wet grinder such as a ball mill, attritor, or sand grinder is used. It is preferable to add it after grinding. Examples of basic colorless dyes as color formers of the present invention include crystal violet lactone, benzoylleucomethylene blue, malachite green lactone, rhodamine B lactam, 3-dialkylamino-7-dialkylaminofluoranes, and 3-dialkylamino-7-dialkylaminofluoranes.
Known compounds such as methyl-2,2-spiropi(benzo-[f]-chromene) can be used alone or in combination, but crystal violet alone is more preferred in the present invention. The color developer layer of silica/magnesia and hydroxybenzoic acid ester compound in the present invention further includes extender pigments such as kaolin, cream, talc, calcium carbonate, zinc oxide, aluminum hydroxide, magnesium oxide,
It can be applied in combination with magnesium carbonate, silica, etc., and is used as a binder to be applied to base paper.
Latex binders such as styrene-butadiene latex and acrylic latex; water-soluble polymer binders such as oxidized starch, etherified starch, carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose, polyvinyl alcohol, casein, gelatin, soy protein, and sodium alginate. Can be used alone or in combination. The amount of these binders added is silica
Magnesia and hydroxybenzoic acid ester compound
10 to 40 parts by weight, preferably 20 parts by weight per 100 parts by weight
~30 parts by weight. The coloring agent is dissolved in a solvent, microencapsulated, and applied to the base paper. As a solvent, natural or synthetic oils can be used alone or in combination. Examples of solvents include cottonseed oil, kerosene, paraffin, naphthenic oil, alkylated biphenyl, alkylated terphenyl, triarylmethane, chlorinated paraffin, and the like. A known microcapsule method can be used to microcapsule the oil in which the coloring agent is dissolved. For example, as a method for manufacturing microcapsules, there is a method using coacelvation as seen in U.S. Patent Nos. 2,800,457 and 2,800,458;
Examples include a method based on polymer precipitation, as described in No. 3,660,304. The microcapsules containing the color former are applied to a sheet such as paper along with various additives, binders, antioxidants, antifouling agents, and surfactants. The pressure-sensitive recording sheet according to the present invention exhibits effects such as no deterioration in color developing ability over time and excellent resistance to discoloration and fading due to nitrogen oxides, light, etc. Among the hydroxybenzoic acid ester compounds used in the present invention, particularly effective compounds are as follows. Methyl para-hydroxybenzoate Ethyl para-hydroxybenzoate Isopropyl para-hydroxybenzoate Butyl para-hydroxybenzoate Heptyl para-hydroxybenzoate Octyl para-hydroxybenzoate Dodecyl para-hydroxybenzoate Benzyl para-hydroxybenzoate Para- 4'-Chlorobenzyl hydroxybenzoate 4'-methylbenzyl para-hydroxybenzoate Phenethyl para-hydroxybenzoate Butyl ortho-hydroxybenzoate Dodecyl ortho-hydroxybenzoate, Phenyl para-hydroxybenzoate Among these, among others Benzyl para-hydroxybenzoate was useful. The present invention will be explained in detail using representative examples, but the present invention is not limited to the examples. All "parts" below refer to "parts by weight." Example: Montmorillonite type clay mineral (ignition loss 5.8 when expressed as weight % based on 110℃ dry matter)
SiO ₂ 78.0, Al ₂ O ₃ 13.0, Fe ₂ O ₃ 1.9, CaO _0.9 ,
MgO _2.6 ) was treated with sulfuric acid to remove Al, Fe, Ca, and Mg ions, yielding treated clay with an aromatic adsorption index of 56.
This treated clay was placed in an aqueous magnesium chloride solution and heat-treated to obtain a silica-magnesia compound consisting of 87.5% SiO ₂ and _12.5% MgO. Bensei acid strength
As a result of investigation by the method described in J.Am.Chem.Soe.78.5490 (1956), the acid strength Ho = +0.8
0.50 mmol/g acid site in the range of Ho=+4.8, 0.27 mmol/g in the range of acid strength Ho=+4.8 to Ho=+9
There are acid points of g, and acid points with acid strength Ho + 0.8 or less are 0.
It was hot. 145 parts of benzylhydroxyethyl para-hydroxybenzoate cellulose water was ground in a ball mill for 2 days. 100 parts of the previously obtained silica-magnesia compound and wet-pulverized benzyl para-hydroxybenzoate solution
Disperse 50 parts in 200 parts of water in which 1 part of sodium pyrophosphate is dissolved, and add 50 parts of 10% oxidized starch and 48%
50 parts of SBR-latex was added to prepare a coating liquid. This coating liquid was applied to a base paper of 50 g/m ² to give a dry weight of 7 g/m ² to obtain a developing paper. The color-forming paper (CB paper) is commercially available Mitsubishi NCR paper N-40, which contains crystal violet lactone and benzoleicomethylene blue as the main color-forming agents.
Upper paper (blue) was used. Table 1 shows the results of a light irradiation test after superimposing these colored paper and developing paper and passing them through a super calendar to develop color.
(Hereinafter, color density and white background density are all expressed as reflection density). In addition, a developer paper blank containing only silica/magnesia as a developer (i.e., the developer paper of the above example except only the hydroxybenzoic acid ester compound) was prepared, and as a comparative example, one using only silica/magnesia as a developer was prepared. A developer paper using the same amount of bisphenol A instead of the hydroxybenzoic acid ester compound was also prepared and tested. From Table 1, compared to when only silica/magnesia is used as a color developer (blank), in the case of the present invention, the density of the supercalendar color itself is improved, and color mixing after light irradiation is significantly prevented. You can see that Next, Table 2 shows the degree of yellowing of the white background of color developer paper due to exposure to NOx gas or sunlight. The developing paper of the present invention exhibits yellowing durability comparable to that of the blank, whereas the comparative example (combined use of silica/magnesia and bisphenol A) showed significant yellowing.
The inventive step of the present invention is recognized. Table 3 shows the NOx fastness of the colored parts. As expected, the NOx fastness of the colored image is significantly improved in the case of the present invention. Table 4 shows the color development speed with a medium-strength calender, and the examples of the present invention are excellent in that the color development speed is fast and the saturation density is also high.

[Table] * Carbon arc lamp fade meter irradiation for 1 hour

【table】

【table】

[Table] Super Calendar coloring shows the value (reflection density) measured with a Macbeth densitometer after coloring was carried out under pressure of 50 kg/cm by combining color-developing paper and color-developing paper. *For discoloration due to nitrogen oxides, generate nitrogen oxide gas using the JISL0855 dye fastness test method for nitrogen oxide gas (fill the gas storage container with water, then drop 300ml of sulfuric acid adjusted to a specific gravity of 1.603 into the gas generator) Place it in a funnel and drop it into sulfuric acid to generate nitrogen oxide, pass it through a trap of 10% sodium hydroxide solution and store it in a gas storage container).After putting a color developer sheet into a desiccator, nitrogen oxide gas is generated. It was injected at a predetermined concentration (ppm) and exposed for 10 or 20 minutes to observe its discoloration. Although the details are omitted, when using crystal violet lactone alone as coloring paper (CB paper) (of course, it is dissolved in a solvent and microencapsulated), the stability of the colored image (Nikko and NOx) further improved.

Claims (1)

[Scope of Claims] 1 A silica-magnesia-based product in which acid clay is treated with acid until the aromatic adsorption index according to formula (1) becomes 40 or more, and then 5 to 50 parts by weight of magnesium ions are introduced per 100 parts by weight of silicon. A pressure-sensitive product made of a combination of a color developer consisting of a solid acid and one or more hydroxybenzoic acid esters represented by formula (2), and microcapsules containing a color former that is a basic colorless dye. Record sheet. Formula (1): Aromatic adsorption index = [(n ²⁰ _D ) A - (n ²⁰ _D ) B] × 10 ⁴ {However, (n ²⁰ _D ) A is a mixture of 30 volumes of toluene and 70 volumes of isooctane at 20°C The refractive index of (n ²⁰ _D )B is the sample obtained by drying the crushed sample at 150℃±5deg・ for 3 hours.
Add 2.00 ml of a mixture of 30 volumes of toluin and 70 volumes of isooctane to 1.00 g, disperse, shake at room temperature for 40 minutes, centrifuge, and collect the supernatant. Refractive index at 20°C}. Formula (2): (However, R represents an alkyl group, an aralkyl group, or an allyl group, and -COOR is at the ortho or para position with respect to -OH). 2. The pressure-sensitive recording sheet according to claim 1, wherein the basic colorless dye is crystal violet lactone alone. 3. The pressure-sensitive recording sheet according to claim 1, wherein the hydroxybenzoic acid ester is benzyl para-hydroxybenzoate.