CA1211627A - Clay mineral-type color developer composition for pressure-sensitive recording sheets - Google Patents

Abstract

ABSTRACT

A color developer composition for pressure-sensitive recording sheets, comprising (1) a color developer which is derived from a clay mineral having a layer structure composed of regular tetrahedrons of silica and which shows (A) a diffraction pattern attributable to the crystals of a layer structure composed of regular tetrahedlrons of slllca when subjected to an electron diffraction analysis, but (B) substantially no diffraction pattern at-tributable to the crystals of said layer structure when subjected to an X-ray dif-fraction analysis, and which (C) contains at least silicon and magnesium and/or aluminum in addition to oxygen, and (2) 0.2 to 2 millimoles, per gram of the components (1) and (2) combined, of at least one metal compound selected from the group consisting of the oxides and hydroxides of calcium, magnesium and zinc. The composition optionally further includes a color developer composed of a dioctahedral montmorillonite clay mineral treated with an acid or a mixture of it with a naturally occurring dioctahedral mont-morillonite clay mineral.

Description

~LZ1~627 Title: CLAY MINERAL-TYPE COLOR DEVELOPER
COMPOSITION FOR PRESSURE-SENSITIVE
RECORDING SHEETS

BACKGRO ND OF THE INVENTIO
1. Field of the Invention This invention relates to a color developer composition which demonstrat~s pronounced color developement effects when used in m~king pressure-sensitive recordling sheet~; which can produce copies byhandwriting, printing or t;yping without the use of conventional carbon paper.

2. Description of t;he Prior Art Pressure-sensitlve recording sheets, except a few special cases, utilize a color development reaction ascribable to the transfer of electrons between a colorle~s organic dye compound having electron donating property and a color developer acting as an electron acceptor (U. S. Patent No. 2,548,366).
Generally, two kinds of dyes which assume different states of coloration are used together as the colorless dye compound. One of them is a dye, such as a triphenylmethane phthalide dye, which forms an intense color immediately upon contact with a solid acid, but the color fades easily (primary color-forming dye). The other is a dye which does not immediately form a color upon contact witll a solid acid but completely develops its color several days thereafter with sufficient fastness to sunlight. An example is a leucomethylene blue dye ~secondary color-forming dye).
Crystal violet lactone (CVL) is a typical primary color-forming dye. As the secondary color-forming dye, benzoyl leucomethylene blue (BLMB) is widely used.
In recent years, fluoran-type green or black dyes, Michler's hydrol derivatives such as Michler's hydryl_para_toluenesulfinate (PTSMH), diphenyl-carbazolylmethane dyes and spirodibenzopyran dyes have `,~k :lZl~L627 also been used either singly or in combination with the aforesaid primary color-forming dye.
Solid acids are generally used as the color developer which is an electron acceptor. It is known that aboYe all, dioctahedral montmorillonite clay mi~erals show excellent color-deYeloping ability. Acid clay and sub-bentonite are especially preferred as thedi-octahedral montmorillonite clay minerals.
It has been known that the specific surface area of montmorillonite cllay minerals such as acid clay and sub-bentonite can be increased to 180 m2/g or hlgher by treating them with acicls, and the acid-treated clay minerals exhibit increasecl color-developing ability with respect to primary color-forming dyes sueh as triphenyl-methane phthalide dyes. For instance, the acid-treated acid clay is generally ref`erred to as activated acid clay, and known widely as a coloring developer for pressure-sensitive recording paper.
Both inorganic and organic aci~s can be used in the acid treatment, but inorganic acids, particularly sulfuric and hydrochloric acids, are preferred because of their reasonable cost and the ease of handling.
The acid-treating conditions are not critical.
If a diluted acid is used, either the treating time becomes longer or the quantity of the required acid increases. On the other hand, if an acid of high concentration is used, either the treating time becomes shorter or the quantity of the acid required becomes smaller. If the treating temperature is high, the treating time can be shortened. Hence, the acid concentration can be freely selected within the range o~
1 to 98%. It is known however that in practice, the acid treatment is preferably carried out at an acid concentration of about 15 to 80% and at a temperature of 50 to 300 C because of the ease of handling.
SUMMARY OF THE INVENTION
According to one aspect of this invention, ~21162~

there is provided a color developer composition for pressure-sensitive recording sheets, comprising (1) a color developer which is derived from a clay mineral having a layer structure composed of S regular tetrahedrons of silica and which shows (A) a diffraction pattern attributable to the crystals of layer structure composed o~
regular tetrahedrons of silica when subjected to an electron diffraction analysis, but ~B) substantially no diffraction pattern attributable to the crystals of said layer structure when subjected to an X-ray diffraction analysis, and which (C) contains at least silicon and magnesium and/or aluminum in addition to oxygen, and (2) 0.2 to 2 millimoles, per gram of the components ~1) and (2) combined, of at least one metal compound selected from the group consisting of the oxides and hydroxides of calcium, magnesium and zinc.
According to another aspect of this invention, there is provided a color developer composition for pressure-sensitive recording sheets, comprising (1) a color developer which is derlved from a clay mineral having a layer structure composed of regular tetrahedrons of silica and which shows (A) a diffraction pattern attributable to the crystals of layer structure composed of regular tetrahedrons of silica when subjected to an electron diffraction analysis, but (B) substantially no diffraction pattern attributable to the crystals of said layer structure when subjected to an X-ray diffraction analysis, and which (C) contains at least silicon and magnesium 16Z~

and~or aluminum in addition to oxygen, (2) a color developer composed of a dioctahed-ral montmorillonite clay mineral treated with an acid or a mixture of it with a naturally occurring di-octahedral montmorillonite clay mineral, and ~ 3) 0.2 to 2 mil:limoles, per gram of the com-ponents (1), (2) and (3) combined, of at least one metal compound selectedl from the group consisting of the oxides and hydroxides of calcium, magnesium and zinc.
BRIEF DESCRIPTION OF THE D~?AWINGS
The attached drawings are graphs showing the relation of the mole ratio between two metal compound9 used in accordance with thils invention to the light resistances of a colored dye.
Figure 1 is a graph showing the relation of the mole ratio between calcium hydroxide and magnesium oxide to the ligh~ resistance of a colored dye in Examples 1 to 5. The total amount of the two metal compounds per gram of the color developer is 0.1 millimole for curve a, 0.2 millimole for curve b, 0.4 millimole for curve c, 0.6 millimole for curve d, 0.8 millimole for curve e, 1.0 millimole for curve f, and 2.0 millimoles for curve ~.
Figure 2 is a gra?h showing the relation o~ th~
mole ratio between calcium hydroxide and zinc oxide to the light resistance of a colored dye in Examples 6 to 10.
Figure 3 is a graph showing the relation of the mole ratio between magnesium hydroxide and zinc oxide to the light resistance of a colored dye ~n Examples 11 to lS.
Figure 4 is a graph showing the relation of the mole ratio between calcium hydroxide and magnesium hy-droxide to the light resistance of a colored dye in Ex-ample 11 and Example 16 to 19.
In Figures 2 to 4, too, the curves a, b, c, d, e, f and ~ refer to the case of the total amount of the two metal compounds being 0.1, 0.2, 0.4, 0.61 0.8, 1.0 and 2.0 millimoles, respectively, as in Figure 1.
The dotted lines in Figures 1 to 3 show the levels of the light resistances of colored dyes in ~2116Z7 Comparative Examples la, 2 and lb, respectively.
DETAILED DESCRIPTION OF THE INVENTION
Color developer (1) Relatively recently, the present inventors found that a color developer ~o be referred to as a color developer (1)~ which is derived from a clay mineral having a layer structure composed of regular tetrahedrons of silica and which shows ~A) a diffraction pattern attributable to the crystals of layer structure composed of regular tetrahedrons of silica when subjected to an electron di~fraction analysis, but (B) substantially no diffraction pattern attributable to the crystals of said layer structure when subjected to an X-ray diffraction analysis, and which (C) contains at least silicon and magnesium and/or aluminum in addition to oxygen has exceIlent color-developing ability for use in pressure-sensitive recording sheets.
The color developer tl) and a method of its production are disclosed in detail in U. S. Patent No.4,405,371 (European Laid-Open Patent Publication No. OQ44645Al).
The color developer ~1) in accordance with this invention can be produced, for example, through the steps o~ acid-treating a clay mineral having a layer structure composed of regular tetrahedrons of silica until its SiO2 content reaches 82 - 96.5% by weight, preferably 85 - 95% by weight, on dry basis (drying at 105C. for 3 hours), contacting the resulting clay mineral, in an aqueous medium, with a magnesium and/or aluminum compound at least partially soluble in the aqueous medium, neutralizing the treated product with an alkali or an acid to form a hydroxide when the soluble compound is not a hydroxide, thereby 1~116Z7 introducing a magnesium and/or an aluminum component into the acid-treated clay mineral, and i~ desired, drying the product.
The compositions of typical clay minerals having the layer structurles composed of re~ular tetrahedrons of silica arle as shown in Table A below, in which the contents (%) of Sio2, A12O3 and MgO as the main components are given.
Table A
__ . , - ~ 2 A123 __ Dioctahe~ral montmorillo--nite (acid clay, bentonil ~ 50 - 70 15 22 1 - 5 ~aolin __~ 40 - 50 32 - 40 O - 1 Halloysite ~ 35 - 45 ~ _ 40 O - 1 Attapulgite 50 - 60 5 - 12 5 - 12 These clay minerals having a layer structures composed of regular tetrahedrons of silica show a unique dif~raction pattern characteristic of the crystals of the layer structure, when subjected to an X-ray diffraetion analysis. In particular, a dif~raction pattern attributable to the crystal faces having Miller's indices Of (020), (200) and (060) appears most distinctly.
According to the present invention, the clay mineral having a layer structure composed of regular tetrahedrons of silica is intensely acid-treated until its SiO2 content reaches 82 - 96.5% by weight, pre~erably 85 - 95% by weight, on dry basis (drying at 105 C. for 3 hours).
It is preferred according to this invention that the acid treatment should be continued until the acid-treated clay mineral (in dry state~ shows substantially no diffraction pattern attributable to the lZ~ Z7 already specified crystal faces of the crystals having a layer structure composed of regular tetrahedrons of silica which the untreated clay mineral has, when sub~ected to an X-ray diffractlon analysis.
s It i~ partlcularly preferred that the acid ~reatment shoulcl be perfol~ed until not only the X-ray diffraction analysis but also an electron diffraction analysis of the acid-treat;ed clay mineral no longer substantially show the chalracteristic diffracti~n pat~erns attr~butable to t;he crystals of the layer structure composed of regular tètrahedrons of silica which the untreated claly mineral has.
The clay mineral which has been acid-treated as above is then contactedl in an aqueous medium with a magnesium and/or an aluminum compound at least partially soluble in the aqueous medium. If the soluble compound i~ not a hydroxide, the treated product is neutralized with an alkali or acid so that a hydroxide of magnesium and/or aluminum is formed therein~thereby introducing a magnesium and/or aluminum component into the acid-treated clay mineral. The product is thereafter dried, if desired.
The foregoing procedure gives the color developer (1) in accordance with this invention which is derived ~rom a clay mineral having a layer structure composed of regular tetrahedrons of silica and which shows (A) a diffraction pattern attributable to the crystals of layer structure composed of regular t~trahedrons of silica when subjected to an electron diffraction ana~ysis, but (B) substantially no diffraction pattern attributable to the crystals of said layer structure when subJected to an X-ray diffraction analysis, and which ~Z~ Z7 (C~ contains at least silicon and magnesium and/or aluminum in addition to oxygen.
Preferably, the color developer (1) used in this invention contains at least silicon and magnesium in addition to oxygen in regard to the requirement (C).
Preferably, the color developer (1) used in this invention, which satLsfies the conditions (A), (B) and (C), further meets the requirement that it contalns silicon and magr~esium and~or aluminum in such proportions that the atomic ratio of '~ilicon to magnesium and/or ~lum~num is fronl 12:1.5 to 12:12, particulary from 12:3 to 12:10 [requirement D].
Typical example~3 of the clay mineral of a layer structure composed of regular tetrahedrons of silica which is used as a raw rnaterial for the production of the color developer (1~1 are given below.
1) Dioctahedral and trioctahedral montmoril-lonite clay minerals such as acid clay, bentonite, beidellite, nontronite and saponite;
2) kaolinite clay minerals such as kaolin, halloysite, dickite and naerite;

3) sepiolite-palygorskite clay mineral3 such as sepiolite, attapulgite and palygorskite;

4) chlorite clay minerals such as leuchten-bergite, sheridanite, thuringite and chamosite;
and 5) vermiculite clay minerals such as vermicu-lite, magnesium vermiculite and aluminum vermiculite.
Preferred among them are dioctahedral mont-morillonite clay minerals such as acid clay, kaolinite clay minerals such as ~aolin and halloysite, and chain clay minerals such as attapulgite.
As already mentioned,it has been the long practice to use the color developer (2), i.e., ~2~16~7 montmorillonite clay minerals, particularly acid clay, which have been treated with mineral acids such as sulfuric, nitric and hydrochloric acids, most commonly sulfuric acid, as a color developer, for pressure sensitive recording sheets.
When an acid Clt~y ~ S treated with such a mineral acid as mentioned above, the acid-soluble basic metal components in the developer, for example, such metal component~; as aluminum, magnesium, iron, calcium, sodium, potassium and manganese (which are present predominantly in the form of oxides or hydroxides) dissolve in the mineral acid, and consequently the SiO2 content of the acid clay increases.
If the acid treatment is performed to a hi8h degree (intensely) to dissolve and remove too much of the baslc metal components, the resulting acid-treated and clay (which also known as activated acid clay) decreased in its color-developing ability with respect to a secondary color development, and the light resistance of a developed color of a primary color development dye (e.g., CVL) in the main is markedly deteriorated.
Accordingly, the degree of acid treatment of acid clay is inherently limitedt and under ths conven-tionally adopted acid-treating conditions, the resulting acid-treated product (activated`clay) has a SiO2 content of about 68 - 78% by weight. Even under considerably rigorous acid-treating conditions, the SiO2 content is at most about 80% by weight.
On the other hand, it has been known of old that the aforementioned montmorillonite clay minerals, kaollnite clay minerals, sepiolite-palygorskite clay minerals, chlorite clay minerals and vermiculite clay minerals have crystals of layer structure composed of regular tetrahedrons of silica, and hence, when examined by X-ray (or electron) diffraction analysis, they give unique diffraction patterns ascribable to ~` 1i2~L;16i~:7 the crystals of layer structure ~Mineralogical Soclety (Clay Mineral Group), London, 1961, The X-Ray Identifica-tion a~d Crystal Structures of Clay Minerals, ed. by G. Brown).
S When those clay minerals having the crystals of layer-structure composed of regular tetrahedrons o~
silica are acid-treated to such an advanced degree that their SiO2 cont~!nts reach 82 - 96.5% by weight, particularly 85 - 95% by l~l/eight, on dry basis (e.g., after a drying a~t 105 C. for 3 hours), their crystals of layer-s~ructure composed of regular tetrahedrons of silica are gradually destroyed as the acid treatment progresses, until, when the SiO2 content reaches 82% by weight or higher, particu]arly 85% by weight or higher, the treated clay minerals no longer show the diffraction pattern characteristic of the crystals of such layer-structure in X-ray (or electron) diffraction analysis.
Of course, the correlations among the degree of acid tr~atment, destruction of the crystals having the la~er-structure and the ultimately occurring substantial disappearance of the characteristic diffraction patterns vary depending on the type and purity of clay minerals, pre treating conditions which may be applied before the acid treatment (e.g., sintering and grinding conditions), etc. and are by no means definite. In all cases, however, as the acid treatment proceeds beyond a certain degree, the destruction of crystals having the layer-structure begins and progresses to result ~ltimately in the substantial disappearance of the diffraction patterns attributable to the aforesaid crystals.
In acid-treating, for example, montmorillonite clay minerals for making a color developer ~color developer (2) used in the invention) for pressure-sensitive recording paper, it has been previouslyconsidered essential to select such acid-treating conditions as would not cause destruction of crystalline lZ~ 7 structure of the clay rninerals, because otherwise the color-developing ability of the color developer would be seriously reduced ~e,g., Journal of Industrial Chemistry (Kogyo Kagaku Zasshi), Vol. 67, No. 7 (1964) pp. 67 - 71~.
Investigations of the pre~ent lnventors, however, led to the discs~very that the color developer (1) for pressure-sensiti~te recor~ing sheets can be produced by (1) i.ntensely acid-treating a clay mineral having a layer structure composed oP regular tetra-hedrons of silica, until its SiO2 content reaches at least 82% by weight, prel~erably at least 85% by weight, on dry basis (drying at ].05C. for 3 hours) (~or convenience, referred to as the first step), and then (2) contacting the resulting clay mineral, in an aqueous medium, with a magnesium and/or an aluminum compound which is at least partially soluble in the aqueous medium, neutralizing the treated product with an alkali or an acid to form a hydroxide when the soluble compound employed is not a hydroxide, thereby introducing into the acid-treated clay mineral a magnesium and/or a aluminum component particularly the magnesium compound, and if desired,drying the product (referred to as the second step for convenience).
It is important in the first step that (A) the clay mineral should be so acid-treated that its SiO2 content should reach 82 - ~6.5%
by weight, preferably 85 - 95% by wei~ht, on dry basis ~drying at 105C. for 3 hours~, and (B) more preferably it should be so acid-treated as to have a SiO2 content within the above-specified range, and furthermore until it shows substantially no diffraction pattern attributable to the crystals of layer-structure composed of regular tetrahedrons of silica possessed by the starting clay mineral (before the acid treatment), when examined by " 1~2116~

X-ray dif~raction.
According to our studies, if the acid-treatment is performed too rigorously until the SiO2 content of the acid-treated clay mineral exceeds 96.5% by weight (on dry basis), the layers themselves which are composed of regular tetrahedrons of silica are excessively destroyed, and it is impossible to re-construct the layered crystalline structures composed of regular tetrahedrons of silica as will be later described, even by the treatment with a magnesium and/or an aluminum compound according to the second step. Hence the resulting clay mineral has markedly inferior color-developing ability to the color developer (1) in the present invention. It is essential, therefore, that the acid-treatment of the first step should be performed to such an extent that the SiO2 content of the acid~treated clay min~ral should not exceed 96.5% b;y weight.
When the acid treatment is continued until the SiO2 content of the treated clay mineral exceeds 95% by weight (on dry basis), the treating conditions become rigorous, and many treatin~ hours are required. In addition to such economical disadvantages, the resulting product does not necessarily exhibit improved color-developing ability, and some types of clay minerals even show a reduced color-developing ability.
Accordingly, the acid treatment is carried out preferably to such an extent that the SiO2 content of the acid-treated clay mineral becomes 85 to 95% by weight, in order to secure economic advantages and to protect the layer composed of regular tetrahedrons of silica from excessive destruction.
The electron diffraction patterns in Figures 1 to 4 of U. S. Patent No. 4,405,371 (European Laid-Open Patent Publication No. 0044645Al) which describes the rearch work of the present inventors on the color developer (1) give the following information.

` 12~16~

For example, the dioctahedral montmorillonite clay mineral occurring in Arizona (U. S. A.) shows a characteris~ic diffraction pattern attributable to the layered crystalline structure (Fig. 1). When it is intensely acid-treated (SiO2 content, about 94% by weight), the diffraction pattern attributable to the crystals substantially disappears in electron diffractometry (Fig. 2). When the acid-treated clay mineral is treat~ed, for example, with an aqueous magnesium chlorilde or aluminum chloride solution according to the second step, neutralized with an aqueous caustic soda solution, washed with water and dried, the product again shows diffraction pattern characteristic of the layered crystalline structure when examined by electron diffractometory, as shown in FigS~ 3 and 4. Thls fact is believed to show that although the cry5tals having the layer-structure composed of regular tetrahedrons of silica are destroyed by the acid-treatment of the first step, the layers themselves remain without complete destructions and that the remaining layers composed of regular tetrahed-rous of silica are re-contructed into crystals by the magnesium and/or aluminum component.
An analysis vf the electron diffraction pattern of the re-constructed crystals shows that the spacin~ of the crystals re-constructed by the magnesium component very closely resembles that of the starting montmorillonite clay mineral ! but that of the crystals re-constructed by the aluminum component isnarrower ~an that of the starting montmorillonite clay minerals.
These facts seem to suggest that the reconstructed crystals, particularly ~hose reconstructed by the aluminum component, differ from the crystals of the starting clay mineral. Nevertheless, the color developer (1) used in this invention which shows the diffraction pattern of the crystals reconstructed by a magnesium or an aluminum component in electron lZ1~627 - 14 _ diffractometry (the product of the second step) exhibits an improved color-developing ability particularly wi~h respect to a primary color-forming dye over the acid-treated product, and also shows an improved color S developing ability with respect to a secondary color-forming dye. Furthermore, the color daveloper (1) scarcely decrea~:es in color-developing ability after s~orage in an at;mosphere kept at a high humidity and a high temperatur~, and evidently, a marked improvement in color-developing ability i.s noted.
Further investigations of the present inventors showed that when a color formed by the color developer (1) is exposed t;o sunlight, particularly to ultraviolet light, the color tends to fade and~or discolor. In an attempt t;o improve the light resistance of the color developer (1), the present inventors made various investigations, and finally found that a color formed by the color developer (1) can be markedly protected from ~ading and discoloration by incorporating a small amount of at least one metal compound selected from the group consisting of the oxides and hydroxides of calcium, magnesium and zinc in the color developer (1) .
The suitable amount of the metal compound to be incorporated in the color developer (1) is 0.2 to 2 millimoles, preferably 0.4 to 1 millimole, per gram of the color developer ~1) and the metal compound combined.
The hydroxide of calcium, the oxide or hydroxide of magnesium and the oxide of zinc are preferred as the metal compound, and calcium hydroxide is especially preferred. These metal oxides or hydroxides can be used either singly or in combination with each other.
When two or more of these metal compounds are used together, (a) a combination of calcium hydroxide and magnesium oxide (or magnesium hydroxide), (b) a combination of calcium hydroxide and zinc oxide, and 21~62~7 (c) a combination Of magnesium hydroxide (or magnesium oxide) and zinc oxide, especially the combinations (a) and (b), are preferred. Advantageously, in these combinations, the mole ratio of calcium hydroxide to magnesium oxide, magnesium hydroxide and/or zinc oxide is adJusted to from 0.9:0.1 to 0.2:0.8. By using the metal compounds in combination as described above, the light resistance of a color formed by the color developer tl) or a mixture of the color developer (1) lQ and the color developer (2) can be further increased, Preferably, the metal compound and the color developer (1) are mixed as uniformly as possible to obtain the composition of this invention~ For this purpose, the metal compound preferably has such a particle size that when its particle size is measured by the Andreasen pipette, the proportion of particles having a particle diameter of not more than 10 microns is at least 70% by weight. It is particularly advantageous that the metal compound contains at least 90% by weight of particles which have a size 325 mesh under according to the Tyler's mesh.
The color developer (1) can be used as a mixture with an acid-treated dioctahedral montmorillonite clay mineral or a mix$ure of it with a naturally occurring dioctahedral montmorillonite clay mineral ~to be referred to as the color dsveloper (2)~ which minerals have heretofore been known as color developers for pressure-sensitive recording sheets. As described in the specification of U. S. Patent No. 4,405,371 (European Laid-Open Patent Publication No. 0044645Al) cited above, a mixture of the color developer (1) and the color developer (2) with the proportion of the color developer (1) being at least 3% by weight based on the mixture, when formed into an aqueous composition for 3S coating on a receiving sheet, has a much lower viscosity than that of an aqueous composition of the color developer t2) alone. Accordingly, the aqueous lZ11~2~7 -- l/j --composition in a high concentration can be coated on the receiving sheet, and the coating operation and drying become easy. When a mixture ~ at least 10% by weight, especially at least 20% by weight, of the color S developer (1), and the color developer (2) is used as a color developer for ~1ressure-sensitive recording sheets, the presence of the color developer (1) increases the color develcping ability of the mixture and its a4ueous composition decrealses in viscosityO Hence, this color developer is very usieful in practical applications.
Even when sUch a color developer mixture is used, the inclusion of the aforesaidl metal compound makes it possible to prevent effectively a color formed by the color developer mixture from fading or discoloratlon.
Accordingly, in the present invention, the metal compound specified above can be incorporated also in the mixture of the color developer (1) and the color developer (2~ in the same way as described above with regard to the color developer (1).
The color developer (2) will be described below in detail.
Color developer (2) The color developer (2) used in this invention may be any of conventional known color developers for pressure-sensitive recording sheets which are composed of acid-treated products of dioctahedral montmorillonite clay minerals such as acid clay and sub-bentonite, or mixtures thereof with naturally occurring dioctahedral montmorillonite clay minerals. The acid-treated products of the montmorillonite clay minerals especially an active clay obtained by acid-treatment of acid clay, are preferred. The acid treatment for production of these is carried out under such conditions that the treated product does not lose the diffraction pattern attributed to the crystals of a layer structure composed of regular tetrahedrons of silica, which the starting clay has.

~2~6~7 The acid-treatment under the relatively mild conditions described above increases the specific surface area of the starting clay mineral. The color developer (2) used in this invention preferably has a specific surface area of at lea~t 180 m2/g.
A typical method for producing the color developer (2) i9; described in the specification of U. S. Patent No. 3,622,354. Preferably, when a secondary color is formed by the reaction of the color developer (2) with benzoyl leuco methylene blue described in the above-cit;ed patent specificatlon, the color developer (2) has a secondary color developing performance K2, defined by~ the following equation, of at least 1.40.

where ~430 and R550 are the reflectances of light having a wavelength of 430 m~ and 550 m~ respectively.
The color developer composition of this invention comprises the color developer (1) or a mixture o~ the color developer (1~ and the color developer (2) and 0.2 to 2 millimoles, preferably 0.4 to 1 millimole, of the aforesaid metal compound per gram of the color developer or developèrs and the metal compound combined. Preferably, the composition is prepared by blending in the dry state the metal compound with a dried product of the color developer (1) or a mixture of it with the color developer (2). When the color developer (2) is used together, it is possible to biend the color developer (2) with the metal compound and then adding the color developer (1) to the mixture.
Alternatively, the metal compound is blended with the color developer (1) and then a suitable amount of the color developer (2) is added to the mixture. Blending can be effected by any known method.

lZ11627 Preferably, the color developer composition of this invention comprising the color developer (1) and the metal compound, or the color developer (1), the color developer (2) and the metal compound has such a particle size that at least 99% by weight thereo~
consists of particles havi.ng a size 325 mesh under in accordance with the Tyler's mesh.
When the color dleveloper composition of this invention is dipped in a lM aqueous solution of ammonium chloride and maintained at: ordinary temperature (for example, 25C) for a suita~ble period of time (for example, 24 hours) preferalbly with occasional shaking, the metal compound blendedl with the color developer (1) or the mixture of the color developers (1) and t2) lS dlssolves in the aqueous ammonium chloride solution.
Hence, the amount of the metal compound in the color developer composition can be determined by this method ~for details, see the testing method described herein after).
The color developer (1) used in this invention is obtained by intensely acid-treating a clay mineral of a layer structure composed of regular tetrahedrons of silica (preferably such that the treated product does not substantially show the diffraction pattern attributed to the crystals o~ layer structure composed of regular tetrahedrons of ilica which the clay mineral ~efore the acid-treatment hasi, and contacting the treated product with at least partially soluble ma~nesium and/or aluminum compound to reconstruct the crystals of the layer structure so ~hat they show a diffraction pattern attributed to the layer structure composed of regular tetrahedrons of silica in electron di~fractometry~ The magnesium and/or aluminum consumed in the reconstruction of these crystals is not dissolved out by the aforesaid treatment with the aqueous ammonium chloride solution, but is still retained in the color developer (1). But that portion of the " ~Z116i~7 magneslum compound used in the reconstruction which remalns free ln the color developer (1) in a very small amount dissolves in the aqueous ammonium chlorlde solution as does the metal compound blended in the color developer (1).
That portion of the magnesium compound used in th~ reconstruction which remains free in the color developer (1) a~ld dissolves in the aqueous ammonium chloride ~olution iS usually ver~ small in amount, and insufficient to improve tlhe light re8istance of a color formed by the color dev&l~Dper (1)~ BUt when combined with the metal compound included in the color developer (1), it serves to increase the light reSistance~
Accordingly, in the present invention, all compounds which are dissolved out ~rom the color developer composition of this invention by treatment with an aqueous ammonium chloride solution and correspond to the aforesaid metal compounds will be dealt wlth as the metal compounds ln accordance with this invention.
The clay minerals used as raw materials for the production of the color developers (1) and (2) contain calcium or magnesium, but calcium and magnesium are not dissolved out by treatment with the aqueous ammonium chloride solution.
In preparing an aqueous composition ~rom the color developer composition for coating on a receiving sheet, the concentration of the color developer composition can be adjusted to about 20 to about 50% by weight. A suitable amount of a water-soluble or water-dispersible binder can be added to the aqueous coating composition.
Examples of the water-soluble binder are starch, carboxy methyl cellulose (CMC), polyvinyl alcohol (PVA), casein and gelatin. Starch and carboxymethyl cellulose are pre~erably used. Examples of the water-dispersible binder are a styrene-butadiene type latex, an acrylic latex, a vinyl 121~27 acetate-type emulsion and vinyl chloride-type emulsion.
The styrene-butadiene ~ype latex is preferred. The combined use of the water-soluble binder and the water-dispersible binder is especially preferred. The amount of the binder used, as solids content, is lO to 30~ by weight, preferably 13 to 20% by weight, basèd on the solids cont~snt of the aqueous coating composition.
The aqueous coating composition may further contain at leaslt one o~ plH adJusting agents, dispersing agents and viscosity ad~usting agents.
The pH ad~ustin,g agents may include the hydroxides and carbonates of alkali metals or alkaline earth metals suclh as sodium hydroxide, lithium hydroxlde, potassium hydroxlde, calcium hydroxide, sodium carbonate and lithium carbonate; sodium silicate;
and ammonia.
Examples of the dispersing agents include polyphosphates such as sodium hexametaphosphate and sodium pyrophosphate, and polycarboxylic acid salts such as sodium polycarboxylate and ammonium polycarboxylate.
As the viscosity adjusting agents, talc, mica and asbestos (Japanese Patent Publication No. 23177/1970), and kaolin, and calcium carbonate (Japanese Patent Pub-lication No. 47992~1980) may be used.
As required, an extender or a color developer other than the color developers tl) and (2) may further be included in the aqueous coating composition in accordance with this invention.
The color developer compositions of this invention have a great color-developing abllity with respect to primary color-forming dyes and secondary color-forming dyes, and their color-developing ability shows only a very low degree of reduction after storage at high temperatures and humidities.
The following Examples and Comparative Examples illustrate the present invention more specifically.

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The various tests used in these examples are described below.
1. Determination o~ the quantity o~ the metal compound About 0.5 g o~ a color developer sample was put in a 100 ml Erle~meyer flask equipped with a ground stopper and precisely wei~3hed beforehand, and dried at 110C for 3 hours. The i~Las~ was then aeain weighed precisely, and lthe w~ight (W g) o~ the sample was 10 determined.
Then, 50 ml of a lM aqueous ammonium chloride solution prepared by using ammonium chloride of special reagent grade was added by a whole pipette. The flask was put ~n a constant temperature vessel equipped with a shaking machine and kept at 25C, and gently shaken for 24 hours. The contents of the flask were separated by a centri~ugal separator.
The supernatant liquid separated was taken in an amount of S ml into a 100 ml Erlenmeyer flask by a whole pipette. A very small amount of aluminum, etc.
was masked with triethanolamine, and the pH of the liquid was adjusted by NH3-NH4Cl bu~fer solution to about 10.
The liquid was then titrated with a 1/100 M standard solu-tion of EDTA using Eriochrome Black T (BT) as an indicator.
The titrated amount (V ml) to the total amount of calcium, ma~nesium and zinc was determined. The amount (mmoles/g) of the metal compound which dissolved at this time from the color developer sample into the lM NH4Cl solution can be calculated from the following equation.

Total amount of dissolved metals = lfoV
where f represents the titer of the 1/100 mole standard solution o~ EDTA.
2. Measurement of the particle di~meter (1) Content of particles having a particle diameter of not more than 10 microns (by the Andreasen pipette method) ~ `

Six grams (after drying at 110C) of a color developer sample was taken into a l-liter narrow-mouthed bottle, and 600 ml of water was added. Then,0.8 g of sodium pyrophosphate of first class reagent grade was added, and the bottle was sealed upO 'rhe bottle was shaken for 60 minutes by a shaking machine at 140 reciprocations per minute (amplitude 8 cm) to disperse the sample. The dispersion was then transferred to an Andreason pipette (JIS Z-8901, DIN 51033) and the pipe-tte was manipulated in accordance with the pipette ope-rating method. Immediate]Ly, a suspension as a blank was collected, and after dryin$ at 110C, its weight was measured (S g). Then, aft;er a certain period of time~
a suspension containing pa,rticles having a particle diameter of not more than 10 microns calculated by the Stokes equation was collected by the pipette. It was dried at 110C, and its weight (W g) was precisely measured. The content (%) of particles having a particle diameter of not more than 10 microns is calculated from the following equation.

Content of particles having W
having a particle diameter of = x 100 not more than 10 microns (%) S
(where S is the weight of the blank and W is the weight of particles having a particle diameter of not more than 10 microns) (2) Content of particles having a size 325 mesh under Fifty grams of a color developer sample (after drying at 110C) was taken into a 500 ml beaker. Water was added and the sample was well dispersed by a glass rod. The dispersion was gently poured little by little onto a 325-mesh sieve, and passed therethrough fully togetAer with flowing water.
All the material left on the sieve was put in a 100 ml beaker using a washing bottle, and dried. The ` 1 2 1 ~ ~ 2 ~

weight (M g) of the solid obtained (a~ter drying at 110C) was measured, and the content (%) of particles having a size 325 mesh under Was calculated from the following equation.
Content of particles (50 - M) having a size 325 = 50 x 100 ~%) mesh under 3. Method of testinlg color-developing ability and met,hod of measuring the viscosity of the coa~in~, composition (1) Preparation of a coating composition One gram of sodium hexametaphosphate was dissolved in 175 g of water, and 100 g (after drying at 110C) of a color developelr sample was added. A 20%
aqueous solution of sodium hydroxide was added to adjust the pH of the solution to about 9.5 (when the pH of the solution before addition of sodium hydroxide exceeds 9.5, the addition of sodium hydroxide is unnecessary).
Then, 15 g of a 20% aqueous solution of starch and 34 g of SBR latex (DoW 620, solids concentration 50%~ were added, and the pH of the solution was again adjusted to 9.5 with a 20% aqueous solution of sodium hydroxide.
Water was further added to adjust the total amount of the slurry to 400 g. It was fully agitated by an agitator to form a uniform dispersion.
(2) Color-developing ability test Preparation of rec_iving sheets The resulting coating slurry was coated on 8 sheets of paper (4 sheets coated at a high rate and 4 sheets coated at a low rate) by means of two coating rods (wire diameter: 0.10 mm and 0.05 mm, respectively).
The coated papers were dried in the air and then dried at 110C for 3 minutes. The amount of the coating solution applied was measured (determined from the dry weight difference between a sample of the uncoated paper and a sample of a uniformly coated portion of the coated ~2~

paper, both samples having the same area). The coated sheets of paper were cut into halves to form two 4-sheet sets (having ~he sam~ coating amount). The amounts of coating o~ the two types were slightly more and slightly less than 6 g/m2.
Initial colo_-developing ability test One of the two 4-sheet sets of receiving sheets waQ put ~n a de3iccator (relative humidity 75%) contain-ing a saturated l~queous solu~ion of sodium chloride, and stored in the dark at 25C. After the lapse of about 24 hours from the coating, it was taken out and exposed indoors (kept constantly at about 25C and a relative humid~ty of about 60%~ for 16 hours, and then subJected to color development. Color development was carried out by the following procedure. The receiving sheets were quperposed on two different types of transfer sheets, either ~1) a transfer sheet coated with microcapsules containing CVL ~Crystal Violet Lactone) which is an instantanéously color-forming leuco dye ~CVL dye sheet) or (2) a commercial transfer sheet coated with micro~
capsules containing a mixture of CVL, BLMB (Benzoyl Leuco Methylene Blue) and a fluoran-type dye (mixed dye sheet);
with their coated surfaces facing each other, and togeth-er inserted between a pair of steel rolls, and revolving the rolls under pressure to rupture the microcapsules completely.
The color-developing ability of each of the receiving sheets was evaluated by measuring the density of the color one hour af~er color formation by means of a densitometer (Fuji Densitometer Model-P, made by Fuji Shashin Film K.K.), and averaging the measured values on four sheets. High densities show high color-developing ability.
The color-developing ability of a sample color developer (density tA)) is expressed by the density tA) on the receiving sheet coated with 6 ~/m2 of the color developer calculated from the density ~Al) of the thinly coated (al g~m ) receiving sheet and the density (A
of the thickly coated (a2 g/m2) receiving sheet.

2~7 In the calculation, because the density and coating amount are in substantially linear relationship (direct proportion) with the receiving sheets coated with an identical sample in the amounts around 6 g/m2, the denslty ~A~ can be determined from the equation below~
Initial color-developi~g ablli ty:

(A) = ~Al~ ~ ~[ ~ ~Al)} (6 - al) a2 ~ a Li8ht resistance test The color-developed sheet used in the initial color-developing ability test was irradiated with an artificial light (carbon arc lamp) for two hours, as set in a weatherometer (Suga Shikenki K.K., Standard Sunshine Weatherometer, W,E-SUN-HC model). The density of the developed color which faded upon the irradlation was measured, The density ~B) of the developed color on the receiving sheet coated with 6 g/m of sample color developer, after fading, was calculated from the similar densities of thinly coated and thickly coated receiving sheets ( ~B~ and ~B~, respectively) as in the foregoing. The light resistance is expressed by the ratio of ~B3 to the initial color-developing density ( ~A) ), i.e., ((B)/~A)).
I~B2~ ~B~} (6 a ) Light resistance: ~B)/~A) (3) Measurement of the viscosity of the coating solution Two hundred grams of the coating solution obtained in ~1) above was transferred to a 300 ml beaker equipped with an agitator (having four perpendicularly crossing blades, 20 mm x 20 mm), and agitated at a speed of 500 rpm in a constant temperature water vessel t; 27 at 25 C for 15 mlnutes. The viscosity of the solutlon~
two minutes a~ter starting of rotation at 60 rpm,was measured by a B-type rotary viscometer.
Comparative Example la Montmorillonite clay occurring in Arizona, U. S. A. was crushed by agitating it together with water to form a 20% slurry. To 500 g of the slurry was add~d 150 8 of 97% sulfuric acid, and further 50 g of water Was added. The mixtUre was heated for 10 hours in a water bath at 95C. During thiS time, the slurry was agitated every 30 minutes to promote the reaction.
A~ter the heating, the treated slurry was suction-filtered, and again water and 150 g of 97% sulfuric acid were added to ad~ust the total amount of the slurry to 15 700 g. It was then acid-treated at 95C for 10 hours.
The treated product was washed with water by filtration, and the cake was put in a pot mill. Water was added, and pulverized in the wet state together with Korean chart pebbles to obtain a 15,~ slurry. (First step) 429 g tsio2 content 60 g) of the resulting slurry (SiO2 content of the dry solid: 93.30%) was heated to 80C, and with stirring, 500 ml of a lM
aqueous solution of magnesium chloride was added dropwlse over the course of about 30 minutes. The mixture was aged for 30 minutes. Then, a 10% aqueous solution of sodium hydroxide was added dropwise over the course of about 30 minutes to perform neutralization. The m~xture was aged for 30 minutes to complete the reaction. The reaction mixture was washed with water by filtration, and the ~iltration cake was dried at 110C. The dried product was pulverized by a small-sized impact pulverizer and coarse particles were removed by a winnowing type classifying machine to obtain fine white particles (color developer la). (Second step) The electron di~fraction pattern and the X-ray diffraction pattern of the color developer (la) are shown in Figures 3 and 7 (Example la) of a U. S. Patent No. 4,405,~71 (European Laid-Open Patent Publication No. 0044645 Al)~

Comparative Example lb Water (350 g) and 250 g of 97% sulfuric acid were added to 100 g of metakaolin produced by calcining a kaolin clay powder occurring in Georgia, U. S. A.
at 700C for 2 hours. The mixture was heated on a water bath at 95 C for 10 hours. During this time, the slurry was agitated every 30 minutes to promote the reaction. Aftel^ the heating, the reaction mixture was suction-filtered, and water and 250 g of 97% sulfuric acid were again added to adjust the total amount of the mixture to 700 g. It was acid-treated at 95C for 10 hours. The treated product was washed with water by filtration, and the filtration cake was put in a pot mill.
Water was added, and the entire mixture was pulverized in the wet state together with Korean chart pebbles to obtain a 15% slurry. (First step) 455 g (SiO2 conltent 60g) of the resulting slurry (SiO2 content of the dry solid: 87.91%) was heated to 80C, and with stirring~ 500 ml of a lM aqueous solution of aluminu~ chloride was added dropwise over the course of about 30 minutes. The mixture was aged for 30 minutes.
Then, 600 8 of a 10% aqueous solution of sodiurn hydroxide was added dropwise over about 45 minutes to perform neutralization. The product was aged for 30 minutes to terminate the reaction. The reaction mixture was washed with water by filtration, and the filtration cake was dried at 110C. It was pulverized by a small-sized impact pulverizer, and coarse particles were removed by a winnowing-type classifier to obtain fine white particles as a color developer (lb). (Second step) The electron diffraction pattern and X-ray diffraction pattern of the color developer (lb) are shown in Figures 5 and 7 (Example 2) of U. S. Patent No. 4,405,371 (European Laid-Open Patent Publication No. 0044645Al).
Referential Example 1 Eight liters of 34% sulfuric acid was added to 4.5 kg of a pulverized product (water content 32%) of acid clay occurring in Nakajo-machi, Niigata-ken, Japan, and the mixture was heated on a water bath at 85C to perform acid treatment (the same as acid treating conditions (B) for sample No. 11 given in Table 1 of U. S. Patent No. 3,622,364)-By filtration, the treated product was washed with water, and the .~iltration cake was dried at 110C, and pulverized. Coarse p~rticles were removed by winnowing to obltain fine white particles as a color developer (2).
The color developer (2) is a known color developer for pressure-sensitive recording sheets.
By the methods described :in the specification o~
U. S. Patent No. 3.622,364, it was found to have a specific surface area of 295 m~/g and a secondary color-developing performance, K2, o~ 1.78.
~omparative Example 2 The color developer (la~ obtained in Compara-tive ~xample la and the known clay mineralt-type color developer (2) obtained in Referential Example 1 were uniformly mixed in a ratio of 50:50 by weight in a fluidizing-type mixer (Supermixer) to obtain a white color developer powder tthis is the same as sample E of Example 1 given in U. S. Patent No. 4,405,371 (European Laid-Open Patent Publication No. 0044645Al).
Example l(la - lg) A powder of calcium hydroxide from which coarse particles had been removed by winnowing was added to the color developer (la) obtained in Comparative Example la in an amount of 0.1, 0.2, 0.4, 0.6, 0.8, 1.0 and 2.0 millimoles respectively per gram of the entire dry mixture (upon drying at 110C). They were uniformly mixed by a fluidizing-type mixer to form a white color developer powder~
Example 2 (2a - 2g) Calcium hydroxide powder and magnesium oxide powder from which coarse particles had been removed by winnowing were uniformly mixed in a mole ratio of o. 75: o, 25 ( 3; 1 ) . The mixture was added to the color developer ~la) obtained in Comparative Example la in a ~otal amount of 0.1, 0.2, 0.4, 0.6, 0.8, 1.0 and 2.0 millimoles respectively per gram of the entire dry mixture(upon dryin8 at 110C), and they were uniformly mixed ln a fluidizing-type mixer to ~orm a white color developer po~lder.
Example 3 (3a-3g) Example 2 was repeated except that the mixing mole rati~ of calcium hydroxide to magnesium oxide was changed to 0.5:0.5 (1:1).
Example 4 (4a-4g) Example Z was repeated except that the mixing mole ratio of calcium hydroxide to magnesium oxide was changed to 0.25:0.75 (1:3).
Example 5 (5a - 5g) Example 1 was repeated except that magnesium oxide was used instead of calcium hydroxide.
Example 6 (6a - 6g) A powder of calcium hydroxide form which coarse particles had been removed by winnowing was added to the color developer powder obtained in Comparative Example 2 in an amount of 0.1, 0.2, 0.4, 0.6, 0.8, 1.0 and 2.0 millimoles respectively per gram of the entire dry mixture (upon drying at 110C~, and they were uniformly mixed in a fluidizing-type mixer to obtain a white develop color developer powder.
Example 7 (7a-7g) Calcium hydroxide powder and zinc oxide powder from which coarse particles had been removed by winnowing were uniformly mixed in a mole ratio of 0.75:0.25 (3:1). The resulting mixture was added to the color developer powder obtained in Comparative Example 2 in an amount of 0.1, 0.2, 0.4, 0.6, 0.8, 1.0 and 2.0 millimoles respectively per gram of the entire ~Zl~Zt~
~ - "

dry mixture (upon drying at 110C), and they were uniforrnly mixed in a fluidizing-type mixer to form a white color developer powder.
Example 8 (8a - Bg) Example 7 was repeated e~cept that the mixing mole ratio of calcium hyd,roxide to zinc oxide was changed to 0.5:0.5 (1:1).
Example 9 (9a - 9g) Example 7 was repeated except that the mixing mole ratio of calcium hydroxide to zinc oxide was changed to 0.25;0.75 (1;3,~.
Exam~le 10 (lOa - lOg) Example 6 was repeated except that zinc oxide was used instead of calci-lm hydroxide.
Example 11 (lla - llg) A powder of magnesium hydroxide from which coarse particles had been removed by winnowing was added to the color developer tlb) obtained in Comparative Exam-ple lb in an amount of 0.1, 0.2, 0.4, 0.6, 0.8, 1.0 and 2.0 millimoles per gram of the entire dry mixture (upon drying at 110C), and they were mixed uniformly in a flui-di~ing-type mixer to form a white color developer powder.
Example 12 tl?a - 12~) A powder of magnesium hydroxide and powder of zinc oxide from which coarse particles had been removed by winnowing were uniformly mixed in a mole ratio of 0.75:0.25 t3:1). The resulting mixture was added to the color developer (lb) obtained in Comparative Example lb in an amount of 0.1, 0.2, 0~4, 0.6, 0.8, 1.0 and 2.0 millimoles respectively per gram of the entire dry mixture (upon drying at 110C), and they were mixed uniformly in a fluidizing-type mixer to obtain a white color developer powder.
Example 13 (13a - 13~
Example 12 was repeated except that the mixing mole ratio of magnesium hydroxide to zinc oxide was changed to 0.5:0.5 ~1:1).

6Z~

Exarl"~le 14 ( 14a - 14g) Exarnple 12 was repeated except that the mixing mole ratio of ma~nesium hydroxide to zinc oxide was changed to 0.25:0.75 (1:3).
Example 15 (15a - lSg) Example 11 was repeated except that zinc oxide waS used instead of magnesium hydroxide.
Example 16 (16a - 16~) A powder of calcium hydroxide from whiCh coarse particles had been removed! by winnowing was added to the powdery developer (lb) obt.ained in Comparative Example lb in an amount of 0.1, 0.2, 0.4, 0.6, 0.8, 1.0 and 2.0 milli moles, respectively, per gram of the entire dry mixture (upon drying at 110C). They were uniformly mixed by a fluidized-type mixer to obtain a white color developer powder.
Example 17 (17a - 17g) A mixture of powdery calcium hydroxide and magnesium hydroxide in a mixing mole ratio o~ 0.75:0.25 ~3:1), from which coarse particles had been removed by winnowing, was added to the color developer (lb) obtained in Comparative Example lb in a total amount of 0.1, 0.2, 0.4, 0.6, 0.8, 1.0 and 2.0 millimoles, per gram of the entire dry mixture (upon drying at 110C), and they were uniformly mixed by a fluidized-type mixer to obtain a white color developer powder.
Example 18 (18a - 13g) Example 17 was repeated except that the mixing mole ratio of calcium hydroxide to magnesium hydroxide ~0 was changed to 0.5:0.5 (1:1).
Example 19 (19a - 19g) Example 17 was repeated except that the mixing mole ratio of calcium hydroxide to magnesium.hydroxide was changed to 0.25:0.75 (1:3).
Example 20 (20a - 20~) Example 1 was repeated except that calcium oxide was used instead of calcium hydroxide.

~21~62~

Example 21 ( 21a - 21g) Example 1 was repeated except that zinc hydroxide was used instead of calcium hydroxide. The zinc oxide used was a powder obtained by adding an aqueous solution of sodium hydroxide to an aqueous solution of zinc sulfate, washing the resulting white precipitate with water, drying it at less than 100C, pulverizing it a~nd removing coarse particles by winnowing.
Example 22 (22a - 22g) Example 1 was re-peated except that zinc oxide was used ins~ead of calcium hydroxide.
Example 23 (23a - 23c) A powder of calc:ium hydroxide with varying particle sizes obtained b~r winnowing was added to the color developer powder (la) obtained in Comparative Example la in an amount of 0.6 millimole per gram of the entire dry mixture (upon clrying at 110C). They were mixed uniformly by a fluicli~ed mixer to obtain a white color developer composition.
Table 10 shows the effect of the content of particles having a particle diameter of not more than 10 microns and the content of particles having a size 325 mesh under in the metal compound on the color-developing performance of each of the resulting colordevelo~er compositions.
Tables 1 to 7 summarize the results of the test of color developing ability of the color developer samples obtained by the above examples. Table 8 shows the results of measuring the content of particles having a particle diameter of not more than 10 microns, the content of particles having a size 325 mesh under, and the viscosities of the coating slurries. Table 9 shows the results of the quantitative analysis of the metal compounds.

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Claims (14)

What is claimed is:

1. A color developer composition for pressure-sensitive recording sheets, comprising (1) a color developer which is derived from a clay mineral having a layer structure composed of regular tetrahedrons of silica and which shows (A) a diffraction pattern attributable to the crystals of a layer structure composed of regular tetrahedrons of silica when subjected to an electron diffraction analysis, but (B) substantially no diffraction pattern attributable to the crystals of said layer structure when subjected to an X-ray diffraction analysis, and which (C) contains at least silicon and magnesium and/or aluminum in addition to oxygen, and (2) 0.2 to 2 millimoles, per gram of the components (1) and (2) combined, of at least one metal compound selected from the group consisting of the oxides and hydroxides of calcium, magnesium and zinc,

2. A color developer composition for pressure-sensitive recording sheets, comprising (1) a color developer which is derived from a clay mineral having a layer structure composed of regular tetrahedrons of silica and which shows (A) a diffraction pattern attributable to the crystals of a layer structure composed of regular tetrahedrons of silica when subjected to an electron diffraction analysis, but (B) substantially no diffraction pattern attributable to the crystals of said layer structure when subjected to an X-ray diffraction analysis, and which (C) contains at least silicon and magnesium and/or aluminum in addition to oxygen, (2) a color developer composed of a diocta-hedral montmorillonite clay mineral treated with an acid or a mixture of it with a naturally occurring dioctahedral montmorillonite clay mineral, and (3) 0,2 to 2 millimoles, per gram of the components (1), (2) and (3) combined, of at least one metal compound selected from the group consisting of the oxides and hydroxides of calcium, magnesium and zinc.

3. The composition of claim 1 or 2 wherein the clay mineral (1) is at least one clay mineral selected from the group consisting of montmorillonite clay minerals, kaolinite clay minerals, sepiolite-palygorskite clay minerals, chlorite clay minerals and vermiculite clay minerals.

4. The composition of claim l for 2 wherein the color developer (1) contains silicon and magnesium and/or aluminum in an atomic ratio, silicon/(magnesium and/or aluminum), of from 12:1.5 to 12:12.

5. The composition of claim 2 wherein the color developer (2) has a specific surface area of at least 180 m2/g.

6. The composition of claim 2 wherein the color developer (2) is an acid-treated acid clay (active clay) or a mixture of it with naturally occurring acid clay.

7. The composition of claim 2 wherein the color developer (2) is an acid-treated dioctahedral mont-morillonite clay mineral or a mixture of it with a naturally occurring dioctahedral montmorillonite clay mineral, and when it is subjected to secondary color development with benzoyl leuco methylene blue, it has a secondary color development performance, K2 defined by the following equation, of at least 1.40, in R430 and R550 represent the reflec-tancesof light having a wavelength of 430 mµ
and 550 mµ respectively.

8. The composition of claim 1 or 2 wherein the color developer (1) is obtained by treating a clay mineral having a layer structure composed of regular tetrahedrons of silica with an acid so that upon drying at 105°C for 3 hours, it has a SiO2 content of 82 to 96.5% by weight, contacting the treated clay mineral in an aqueous medium with a magnesium and/or an aluminum compound at least partly soluble in the aqueous medium, neutraliz-ing the product with an alkali or an acid to form a hydroxide when the soluble compound is not a hydroxide thereby to introduce magnesium and/or aluminum into the acid-treated clay mineral, and if desired, drying the product.

9. The composition of claim 1 or 2 wherein the color developer (1) is obtained by treating a clay mineral having a layer structure composed of regular tetrahedrons of silica with an acid until by an X-ray analysis, the acid-treated clay mineral does not substantially show the diffraction pattern attributable to the crystals of the layer structure composed of regular tetrahedrons of silica which the clay mineral before the acid treatment has.

10. The composition of claim 1 or 2 wherein the amount of the metal compound is 0.4 to 1 millimoles per gram of the com-ponents (1) and (2) combined or the components (1), (2) and (3) combined.

11. The composition of claim 1 or 2 wherein the metal compound is calcium hydroxide.

12. The composition of claim 1 or 2 wherein the metal compound has such a particle size that at least 70% there of consists of particles having a particle diameter of not more than 10 microns when it is measured by the Andreasen pipette method.

13. The composition of claim 1 or 2 wherein the metal compound contains at least 90% by weight of particles having a size 325 mesh under in accordance with the Tyler's mesh.

14. The composition of claim 1 or 2 which contains at least 99% by weight of particles having a size 325 mesh under in accordance with the Tyler's mesh.