Recording Sheet And Color Developer Therefor

Abstract

A recording sheet comprising a support having coated thereon a layer of color developer comprising a metal compound of a polymer, said polymer being a reaction product of an aromatic carboxylic acid with an aldehyde or acetylene, said color developer being capable of forming a distinct color when contacted with a color former.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a recording sheet and a color developer therefor, and more particularly to a recording sheet having coated thereon a novel color developer layer and to a novel color developer for the recording sheet.

2. Description of the Prior Art

There have been known recording sheets utilizing a color reaction of a colorless organic compound (hereinafter, referred to as a "color former") and an adsorbent material capable of forming a distinct color when contacted with the color former.

As recording sheets using the phenomenon, a pressure-sensitive recording sheet (U.S. Pat. Nos. 2,505,470; 2,505,489; 2,550,471; 2,548,366; 2,712,507; 2,730,456; 2,730,457; 3,418,250 etc.) and a heat-sensitive recording sheet have been well known. Further, a printing method has been known wherein an ink containing the color former is applied to the color developer sheet, either through a medium such as a stencil, or not.

In all cases, the above phenomenon of the color reaction between the color former and the color developer are utilized under pressure with a pen or stylus, under heat, etc.

The color former may be dissolved in a solvent such as chlorinated diphenyl, chlorinated paraffin or other organic solvents. The solution may be dispersed in a binder and/or may be microencapsulated, and then coated onto a support such as paper, plastic films, resin-coated papers., etc.

In the case of a heat-sensitive recording sheet, the color former may be coated onto the support together with a thermofusible material such as acetanilide which is melted under heating to dissolve the color former.

On the other hand, the color developer is dissolved or dispersed in water or an organic solvent together with a binder such as styrene-butadiene rubber latex and then coated on or impregnated into a base support before or directly before recording.

The color former and color developer may be coated onto the same surface or opposite surfaces of a support, or onto different supports.

Usually, after the color developer is coated onto the support, a desensitizer is locally coated thereon in order that unnecessary color formation on certain surface portions is prevented (U.S. Pat. No. 2,777,780). Another embodiment of the prevention of color formation is to locally coat the color developer onto the support or onto the coated layer containing the color former without using the desensitizer.

As the above described color developer, clays such as acid clay, active clay, attapulgite, zeolite, bentonite, etc.; phenol resins (U.S. Pat. Nos. 3,516,845; 3,540,911) and organic compounds such as succinic acid, tannic acid, gallic acid or phenol compounds (U.S. Pat. No. 3,244,548) are known. Such organic compounds are not practically employed for the reason that the color developing ability of the color developer sheet (which is a support having coated thereon the color developer) is very low and the color developed on the sheet is low in light resistance although the compound can be very easily handled in manufacturing the color developer sheet.

Further, in cases where the above color developer is locally coated onto a support to form a color developer sheet, if a large amount thereof (7-10 g per 1 m.sup.2 of the support) is coated, the color developer sheet cannot form sufficient color when contacted with the color former. As a result, the localized coating method is limited in utility.

In this case, since the locally-coated portions of the color developer sheet are thicker than the other portions, the color former, coated on another support, when contacted with the color developer sheet, is locally pressurized to form unpreferable color (hereinafter, referred to as "fog").

SUMMARY OF THE INVENTION

The inventors have found that all defects of the color developer sheet and ink using the above-described organic compound can be completely removed by using a metallic compound of a polymer of an aromatic carboxylic acid with an aldehyde or acetylene. That is, the present inventors have found that a color developer composed of a metallic compound of a polymer of an aromatic carboxylic acid and an aldehyde or acetylene is far stronger in color developing ability than an aromatic carboxylic acid, or a metallic compound, and that the color formed on such a color former sheet is stronger in light resistance.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The color developer of the present invention, that is, the metal compound of a polymer of an aldehyde or acetylene and an aromatic carboxylic acid having at least one hydroxyl group is a product produced by the reaction of an alkali metal salt of the polymer of an aldehyde or acetylene and an aromatic carboxylic acid having at least one hydroxyl group with a water-soluble metal salt in a solvent in which both reagents are soluble. In this case, the ratio of the alkali metal salt and water-soluble metal salt is not limited particularly, but a molar ratio of 1 to 1 is preferred. Preparation of the alkali metal salt of the polymer used in the above-mentioned reaction can be carried out in a known manner, for example, by reacting the above-mentioned polymer with an alkali metal hydroxide or carbonate.

Illustrative of the polymer of an aldehyde and an aromatic carboxylic acid having at least one hydroxyl group used in the present invention are a salicylic acid-aldehyde polymer, a p-hydroxybenzoic acid-aldehyde polymer, a 2,6-dihydroxybenzoic acid-aldehyde polymer and a salicylic acid-acetylene polymer.

The polymer applicable to the invention is a polymer of an aldehyde and an aromatic carboxylic acid having at least one hydroxyl group, while metal compounds of phenol-aldehyde polymers mentioned in Japanese Patent No. 511,757, phenol-acetylene polymers, maleic acid-rosin resins and partly or extensively hydrolyzed styrene-maleic anhydride polymers have no developing capacity.

The aromatic carboxylic acid used in the present invention is such a compound as having at least one carboxyl group per aromatic nucleus and includes, for example, benzoic acid, o-nitrobenzoic acid, m-nitro benzoic acid, p-nitrobenzoic acid, o-chlorobenzoic acid, m-chlorobenzoic acid, p-chlorobenzoic acid, o-toluic acid, m-toluic acid, p-toluic acid, o-bromobenzoic acid, m-bromobenzoic acid, p-bromobenzoic acid, o-iodobenzoic acid, m-iodobenzoic acid, p-iodobenzoic acid, 4-methyl-3-nitrobenzoic acid, 2-chloro-4-nitrobenzoic acid, 2,3-dichlorobenzoic acid, 2,4-dichlorobenzoic acid, p-isopropyl-benzoic acid, 2,5-dinitrobenzoic acid, 3,4-dinitrobenzoic acid, 3,5-dinitrobenzoic acid, p-tert-butylbenzoic acid, N-phenyl-antranillic acid, 4-methyl-3-nitrobenzoic acid, 4-acetyl-benzoic acid, salicylic acid, 5-tert-butyl-salicylic acid, 3-phenyl-salicylic acid, 3-methyl-5-tert-butyl-salicylic acid, 3,5-di-tert-butyl-salicylic acid, 3,5-ditert-amyl-salicylic acid, 3-cyclohexyl-salicylic acid, 5-cyclohexyl-salicylic acid, 3-methyl-5-isoamyl-salicylic acid, 5-isoamyl-salicylic acid, 3,5-di-sec-butyl-salicylic acid, 5-nonyl-salicylic acid, 3-methyl-5-lauryl-salicylic acid, m-hydroxyl-benzoic acid, p-hydroxybenzoic acid, 3,5-dinitrosalicylic acid, 2-hydroxyl-3-methyl-benzoic acid, 2,4-cresotinic acid, 2,5-cresotinic acid, 2,3-cresotinic acid, 2,4-dihydroxy-benzoic acid, 2,5-dihydroxybenzoic acid, 2,6-dihydroxybenzoic acid, 1-naphthoic acid, 2-naphthoic acid, 1-hydroxyl-2-naphthoic acid, 2-hydroxyl-3-naphthoic acid, 2-hydroxyl-1-naphthoic acid, 5,5'-methylenesalicylic acid, thiosalicylic acid, trimellitic anhydride, anacardic acid, benzoic anhydride, 2-carboxybenzaldehyde, diphenic acid, etc. Above all, aromatic carboxylic acids having at least one hydroxyl group in the structure are effective.

Illustrative of the metal salts used in the invention are salts of metals of Group Ib of the Periodic Table such as copper and silver, Group IIa such as magnesium and calcium, Group IIb such as zinc, cadmium and mercury, Group IIIa such as aluminum and gallium, Group IVa such as tin and lead, Group IVb such as chromium and molybdenum, Group VIIb such as manganese and Group VIII such as cobalt and nickel. In particular, salts of zinc, tin, aluminum and nickel are preferably used.

For the production of the color developer sheet according to the invention, salts of the foregoing metals with inorganic acids such as chloride, sulfate and nitrate, and salts of organic acids such as acetate and oxalate are used.

When each of the alkali metal salts of the polymer and the metal salts are individually applied to supports such as paper, there is found no developing capacity.

The color developer sheet of the invention is produced by dispersing in a binder at least one metal compound of a polymer formed by reaction of the alkali metal salt of the polymer and the metal salt as they are reacted, or after being purified, and then applying the dispersion to a support such as paper or a plastic film, etc.

Further, for the purpose of increasing color developing ability and light resistance, an inorganic pigment may be added to the color developer. The inorganic pigment comprises aluminum silicate, zinc silicate, lead silicate, tin silicate, colloidal hydrated aluminum silicate, zeolite, bentonite, kaolinite active clay, acid clay, talc and the like. The amount of inorganic pigment employed is not critical, for example, more than 1 part by weight, preferably 10 to 1000 parts by weight per 100 parts by weight of the metal salt of polymer may be used.

As the solvent for the color developer of the invention, there are water or an organic solvent such as methanol, ethanol, butanol, ethyl acetate, butyl acetate, benzene, toluene, acetone, tetrahydrofuran or methylene chloride. Water and organic solvents may be mixed. A preferable solvent is capable of dissolving the organic carboxylic acid. In case of adding the inorganic pigment, it may be dispersed in water, the organic solvent, the solution or the dispersion.

The thus-prepared solution or dispersion can be coated on a support, if necessary, together with a binder such as gelatin, casein, gum arabic, ethyl cellulose, styrene-butadiene copolymer, nitrocellulose, styrene-butadiene latex, methylmethacrylate-butadiene latex, etc. The amount of the binder can be easily decided by one skilled in the art. The coating method may be a roll coating method, an air knife coating method, a blade coating method, a flexo coating method, a gravure coating method, etc. It should be noted that the coated layer of color developer can be maintained on the support even if the binder is not present in the layer.

The amount of the color developer coating composition is not specifically limited to obtain sufficient color. For example, it is more than 0.1 g/m.sup.2, preferably 0.5-5 g/m.sup.2. The upper limit of coating amount is not limited from the point of view of color developing activity, and the above range is only due to economic reasons.

The color developer composition can be coated onto a support by all kinds of coating methods because the present invention is basically characterized by using the metal compound of the polymer.

As another embodiment for preparing a color developer composition, the binder is dissolved in the organic solvent and a plasticizer is added and then the metallic compound of the polymer is dissolved or dispersed in the resulting solution.

The plasticizer may comprise esters of phosphoric acid, phthalic acid, adipic acid or sebacic acid (e.g. tributyl phosphate, dibutyl phthalate, dioctyl phthalate, butyl adipate, dibutyl sebacate); hydrocarbons such as chlorinated paraffin; and glycerides of unsaturated fatty acids such as castor oil.

In this case, for the purpose of stabilizing the color developer composition which may be used as a coating ink, an organic carboxylic acid or a metal salt thereof may be added to the composition.

Organic carboxylic acids and metallic compounds thereof used in the present invention are as follows:

Organic carboxylic acids having six or more carbon atoms such as caproic acid, caprylic acid, capric acid, heptanoic acid, pelargonic acid, n-heneicosanic acid, behenic acid, n-undecylenic acid, n-tridecylenic acid, n-pentadecylenic acid, lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, n-nonadecylenic acid, arachidinic acid, n-tricosanoic acid, n-dotriacontanoic acid, n-hentriacontanoic acid, n-hexatriacontanoic acid, n-pentacosanoic acid, n-heptacosanoic acid, lignoceric acid, linolenic acid, linoleic acid, cerotic acid, montanic acid, n-nonacosanoic acid, melissic acid, n-tertrameriacontanoic acid, celloplastic acid, n-octatriacontanoic acid, n-hexatetracontanoic acid, oleic acid, stearolic acid, .alpha.-chlorolauric acid, .alpha.-chlorostearic acid, .alpha.-bromomyristic acid, octane-1,8-dicarboxylic acid, dodecane-1,12-di-carboxylic acid, 2,4-decane dienic acid, 2-oxy-2,4-dimethyl-pentanoic acid, benzoic acid, o-toluic acid, m-toluic acid, p-toluic acid, o-chlorobenzoic acid, m-chlorobenzoic acid, p-chlorobenzoic acid, o-bromobenzoic acid, p-nitrobenzoic acid, salicylic acid, m-oxysalicylic acid, p-oxysalicylic acid, anisic acid, gallic acid, phthalic acid, trimellitic acid, diphenic acid, phenyl acetate .delta.-phenyl-n-valerianic acid, p-isopropyl benzoic acid, 2,4-cresotinic acid, 2-hydroxy-3-methyl benzoic acid, 1-naphthoic acid, 2-naphthoic acid, 1-hydroxy-2-naphthoic acid, 2-hydroxy-3-naphthoic acid, etc., and metallic salts thereof as described below are effective.

As a metal there are sodium, lithium, potassium, magnesium, calcium, zinc, cadmium, aluminum, tin, lead, chromium, manganese, cobalt, nickel, etc.

For manufacturing the color developer sheet of the present invention, at least one metallic compound of a polymer produced by a reaction of the above described alkaline salt of polymer and the above water soluble metallic salt, as it is in the reaction mixture or preferably after it is separated and purified, is dispersed in a binder together with at least one organic carboxylic acid or its metallic salt and is coated onto a support such as paper, synthetic paper, film etc.

In this case, the amount of organic carboxylic acid or its metallic salt to be used is more than 10 parts per 100 parts of the above color developer, desirably 20 to 200 parts, by weight.

Each component is dissolved or dispersed by means of a ball mill or a sand mill. The prepared color developer ink can be locally applied to a support.

A color developer sheet and the color developer of the invention can be used in combination with conventional color formers such as crystal violet lactone, benzoyl leuco methylene blue, malachite green lactone, rhodamine B lactam, fluoranes (U.S. Pat. Nos. 3,501,331; 3,514,311; 3,540,911), spiropyrans (U.S. Pat. No. 3,293,060), mixtures thereof and the like.

Modification of the present invention can be easily carried out by those skilled in the art in accordance with conventional information, techniques and the like.

The color formers for pressure-sensitive copying paper are ordinarily employed in combination in order to secure the instantaneous color forming property and light fastness of the colored image. For example, a combination of instantaneous color forming crystal violet lactone as a primary color former and benzoyl leucomethylene blue having an excellent light fastness has been most well known, however, the colored image obtained by contacting this combination of color formers with an aromatic carboxylic acid tends to disappear, when it is allowed to stand in a room or is exposed to sunlight, since crystal violet fades before benzoyl leuco-methylene blue is color formed. However, such a defect as described above is removed in the present invention, since, on the color developer sheet using a metallic compound of a polymer, crystal violet lactone is strong in light fastness and does not fade before benzoyl leuco methylene blue is color formed. This will be clear from the light-fastness of crystal violet lactone in the below described Examples.

In comparison with conventional clay-coated papers, the color developer sheet of the present invention has the following advantages:

The clay sensitivity of conventional clay-coated paper tends to decrease when allowed to stand in air, because materials in the air are adsorbed on the active point of the clay. That is, the color developing ability of conventional color developer sheets is remarkably lowered with time.

In the color developer sheet of the present invention, such defect has been improved. And, in the case of manufacturing a color developer sheet in accordance with the present invention, sufficient color developing ability and other properties necessary to the color developer sheet for pressure sensitive paper can be satisfied with smaller coating amounts than in the conventional clay paper. That is, the amount of color developer of the present invention to be coated is sufficient with 0.1 to 5 g/m.sup.2 while in the conventional clay paper the amount to be coated is 7 to 10 g/m.sup.2. Thus, it is possible to make the present color developer sheet by a size spray coating by means of a machine since only a small amount is necessary and since the physical properties of the liquid can be freely varied different from clay, which results in a remarkable effect not only on performance but also on production.

Furthermore, the color developer of the present invention can give similar color developing ability even with smaller amounts (by about 2 g/m.sup.2) to be coated, if a natural or synthetic high molecular weight substance or a water-repellant is previously coated onto the surface of the paper support.

Other advantages of the present invention will be understood as follows:

Improvement of the yellowing:

The surface of the color developer sheet is difficult to yellow by irradiation with sunlight or when allowed to stand in a room. Hence, the instant pressure sensitive recording paper, using a metallic salt of a polymer, is more improved in article value.

Improvement of strength and quality of coated layer:

By using an organic carboxylic acid or its metallic salt, the amount of binder necessary to obtain the same film strength is decreased and the film quality becomes smooth in feeling and hence the article value is more elevated. For improvement of film quality, an aliphatic carboxylic acid or its metallic salt is particularly effective.

The present invention will be further illustrated using a pressure sensitive recording paper with the following Examples.

The effect of the color developer sheet of the present invention was confirmed with the following color former sheet, prepared as follows.

Preparation of Color Former Sheet

Microcapsules containing a color former were manufactured, for example, according to the specification of U.S. Pat. No. 2,800,457, as follows:

10 parts by weight of acid-treated pigskin gelatin and 10 parts by weight of gum arabic were dissolved in 400 parts by weight of water at 40.degree.C and 0.2 parts by weight of Turkey red oil was added thereto as an emulsifier, and 40 parts by weight of color former oil were emulsified and dispersed therein.

The color former oil is 2 percent of crystal violet lactone or 3-dibenzyl-amino-7-diethylaminofluorane dissolved in an oil consisting of 4 parts by weight of chlorinated diphenyl and 1 part by weight of kerosene. The emulsification was stopped when the size of the oil droplets became 5 microns on an average. Water at 40.degree.C was added thereto to 900 parts by weight in total and the stirring was continued. At this time attention must be paid so that the liquid temperature does not lower to below 40.degree.C. Next, 10 percent acetic acid was added thereto to adjust the pH of the system to 4.0 to 4.2 and to cause coacervation. The stirring was further continued and, after 20 minutes, the system was cooled with ice to gelate a coacervate film deposited around an oil droplet. When the liquid temperature became 20.degree.C, 7 parts by weight of 37 percent formaldehyde were added thereto and at 10.degree.C, a 10 percent aqueous solution of caustic soda was added to adjust the pH to 9. At this time, addition of caustic soda must be carried out with sufficient attention.

The liquid temperature was raised to 50.degree.C by heat under stirring for 20 minutes. The microcapsules thus obtained were controlled to 30.degree.C and thereafter were coated onto a 40 g/m.sup.2 paper in 6 g/m.sup.2 as solid content and dried. Also, in case of other color formers, the recording paper was manufactured in the same manner as described above.

In the following Examples, "part" means "part by weight."

EXAMPLE 1

138 g of salicylic acid and 325 g of 37% formaldehyde were polymerized by a known method, heating at 95.degree.-97.degree.C for 1 hour using 250 g of 12N sulfuric acid as a catalyst. 1 basic mol of this polymer was dissolved in 500 ml of warm water in which 1 mol of sodium hydroxide was dissolved. To this solution was gradually added, with agitation, 500 ml of warm water in which 1 gram equivalent of a metal salt as shown in Table 1 had been dissolved. Then 50 g of a binder shown in Table 1 was dissolved or dispersed in 500 ml of warm water and added thereto to give a coating solution. The coating solution was applied to a paper of 40 g/m.sup.2 to give a solid content of 5 g/m.sup.2 followed by drying to form a developer sheet.

EXAMPLE 2

A polymer was obtained by a method similar to that of Example 1. 1 basic mol of the polymer was dissolved in 500 ml of warm water in which 1 mol of potassium hydroxide had been dissolved. To this solution was gradually added, with agitation, warm water in which 1 gram equivalent of a metal salt as shown in Table 1 had been dissolved, thus forming a precipitate. The precipitate was filtered, washed several times with water dried and pulverized.

Then 10 grams of a binder (as shown in Table 1) was dissolved or dispersed in 100 ml of a solvent (see Table 1) in which 30 g of the finely-divided metal compound of the polymer was dispersed. The resulting coating solution was applied to a paper of 40 g/m.sup.2 to give a solid content of 5 g/m.sup.2, followed by drying.

EXAMPLE 3

154 g of 2,6-dihydroxybenzoic acid and 325 g of 37% formaldehyde were polymerized by a known method, heating at 95-97.degree.C for 1 hour using 250 g of 12N sulfuric acid as a catalyst.

1 basic mol of this polymer was dissolved in 500 ml of warm water in which 1 mol of sodium hydroxide had been dissolved. To this solution was gradually added, with agitation, 500 ml of warm water in which 1 gram equivalent of a metal salt shown in Table 1 had been dissolved. Then 50 g of a binder, as shown in Table 1, was dissolved in 500 ml of warm water or dispersed therein, and added thereto to give a coating solution. The coating solution was applied to a paper of 40 g/m.sup.2 to give a solid content of 5 g/m.sup.2, followed by drying to form a developer sheet.

Test result:

1. A crystal violet lactone-containing microcapsule-coated paper was stacked on the developer sheets of Examples 1, 2 and 3 to which a load pressure of 600 kg/cm.sup.2 was then applied. It was then allowed to stand in the dark for 1 hour and the spectral absorption curve was measured between a wavelength of 700-400 m .mu.. The developing capacity of the developer sheet was found by a density (D.sub.1) at its absorption maximum (wavelength 610 m .mu.).

2. A 3-dibenzylamino-7-diethylaminofluoran-containing microcapsule-coated paper was stacked on the developer sheets of Examples 1, 2 and 3 and color formed in a manner similar to the foregoing comparison test (1). After the passage of 1 hour in the dark, the spectral absorption curve was measured between wavelengths of 700-400 m .mu.. The developing capacity of this developer sheet was found by a density (D.sub.2) at its absorption maximum (wavelength 600 m .mu. ).

The results are shown in Table 1, in which a polymer of salicylic acid and formaldehyde is shown by P-1 and a polymer of 2,6-dihydroxy-benzoic acid and formaldehyde is shown by P-2. ##SPC1##

EXAMPLE 4

138 parts of salicylic acid and 325 parts of 37% formaldehyde were polymerized by adding 250 parts of 12N sulfuric acid as a catalyst thereto under heating at 95.degree.-97.degree.C for 1 hour to provide a polymer (P-1).

1. The polymer P-1 was dissolved in 4 parts of sodium hydroxide dissolved in 100 parts of warm water to prepare the solution of polymer. To the polymer solution, 7 parts of tin chloride dissolved in 100 parts of warm water was added dropwise with stirring to provide a tin compound of the polymer, followed by filtration, washing and drying to obtain a powder of a tin compound of the polymer. On the other hand, a solution (hereinafter referred to as Varnish A) was prepared by mixing 15 parts of styrene-butadiene copolymer, 60 parts of toluene and 25 parts of petroleum naphtha. A color developer ink 1 was obtained by mixing 25 parts of the tin compound of the polymer (P-1) and 70 parts of Varnish A.

2. A nickel compound of the polymer (P-1) was prepared by the same method as above, using 4 parts of sodium hydroxide, 15 parts of P-1 and 6 parts of nickel sulfate. A color developer ink 2 was obtained by mixing 20 parts of the nickel compound of P-1, 7 parts of titanium oxide and 73 parts of Varnish A.

3. A zinc compound of the polymer (P-1) was prepared, by the same method as above, using 4 parts of sodium hydroxide, 15 parts of P-1 and 5 parts of zinc chloride. A color developer ink 3 was obtained by mixing 25 parts of the zinc compound of P-1, 3 parts of aluminum silicate and 72 parts of Varnish A.

154 parts of 2,6-dihydroxybenzoic acid and 325 parts of 37% formaldehyde were polymerized by adding 250 parts of 12N sulfuric acid thereto under heating 95.degree.-97.degree.C for 1 hour to obtain a polymer (P-2). A solution (hereinafter referred to as Varnish B) was prepared by mixing 10 parts of nitrocellulose, 30 parts of butyl acetate, 40 parts of ethyl alcohol and 20 parts of methyl cellosolve.

4. A tin compound of the polymer P-2 was prepared, by the same method as above, using 4 parts of sodium hydroxide, 16 parts of P-2 and 5 parts of tin sulfate. A color developer ink 4 was obtained by mixing 26 parts of the tin compound of P-2 and 74 parts of the Varnish B.

5. A zinc compound of the polymer (P-2) was prepared, by the same method as above, using 4 parts of sodium hydroxide, 16 parts of P-2 and 6 parts of zinc chloride. A color developer ink 5 was obtained by mixing 20 parts of the zinc compound of P-2, 7 parts of magnesium carbonate and 73 parts of the Varnish B.

Comparative Tests

The color developer inks prepared as above were each diluted with a solvent shown in the following table so as to have a viscosity of about 100 centipoises, and then were each applied to a paper in a dry thickness of 2 g/m.sup.2 by a flexo or a gravure printing method. The obtained color developer sheets were piled on color former sheets, and pressurized under 600 kg/m.sup.2 to form color images.

After allowed to stand in the dark for 1 hour, spectral absorption curves of the color images were measured at wave lengths of 400 - 700 m .mu., and a density at the maximum absorption was defined as a color developing ability. The results were shown in the following Table 2.

TABLE 2

Density Crystal Solvent for Printing Violet No. Solution Method Lactone fluorane 1 Toluene Gravure 0.89 0.78 2 " " 0.67 0.64 3 " " 0.67 0.59 4 Isopropyl alcohol Flexo 0.76 0.68 5 " " 0.66 0.62

As is apparent from the above table, the color developer ink of the invention gave more excellent color developing ability even in the case of a thin coating (2 g/m.sup.2).

Further, even if the color images were wet with water, the color density was not lowered.

EXAMPLE 5

250 g of 12N sulfuric acid was added to 1 mole of the aromatic carboxylic acid shown in the following Table 3 and 325 g of a 37% aqueous formaldehyde solution and was heated at 95.degree. to 97.degree.C under stirring for 1 hour. 1 basic mole of a polymer thus synthesized was dissolved in 500 ml of a 2N aqueous caustic soda solution. Then, 1 g equivalent of the water-soluble metallic salt (Nos. 1-7 and 10-17) shown in Table 3 was dissolved in 500 ml of warm water and was slowly added to the above alkaline solution of a polymer under stirring. Immediately the solution became muddy for precipitation of white or tinted solid. The stirring was continued for a while and the solid was dispersed well. Next, 70 g of the binder shown in Table 3 was dissolved or dispersed in 700 ml of warm water and thereafter was added to the above dispersion under stirring and then 100 g of inorganic pigment, having passed a sieve of 325 mesh, and shown in Table 3 was added and dispersed therein. The coating liquid manufactured as above was coated on a 40 g/m.sup.2 paper by means of a coating rod in a solid content of 5 g/m.sup.2 and dried to obtain the color developer sheet of the present invention.

COMPARATIVE EXAMPLE 5

1 basic mole of a copolymer obtained in the same manner as in Example 5 was dissolved in 500 ml of 2N aqueous caustic soda solution, and 1 g equivalent of the water-soluble metallic salt (Nos. 1-7 and 10-17) shown in Table 3 dissolved in 500 ml of warm water was gradually added thereto under stirring. The solution became muddy immediately for precipitation of white or tinted solid. The stirring was continued for a while and the solid was well dispersed.

Next, 50 g of the binder was dissolved or dispersed in 700 ml of warm water and thereafter was added to the above dispersion under stirring.

The coating liquid thus manufactured was coated onto a 40 g/m.sup.2 paper in a solid content of 4 g/m.sup.2 by means of a coating rod and dried to obtain a color developer sheet for comparison.

EXAMPLE 6

1 basic mole of a polymer obtained in the same manner as in Example 5 was dissolved in 500 ml of 2N aqueous caustic soda solution. Then, 1 g equivalent of the water-soluble metallic salt (No. 8-9) shown in Table 3 was dissolved in 400 ml of warm water and gradually added to the above alkaline solution of polymer under stirring. Immediately a white or tinted solid was precipitated.

In order to complete the precipitation, the system was allowed to stand for a while and then filtered. The solid obtained was washed with water and thereafter dried and ground to obtain a fine powder passing a sieve of 325 mesh.

Next, 10 g of the binder, as a solid, was dissolved or dispersed in 100 ml of the solvent shown in Table 3 and 20 g of the above metallic compound of polymer and 10 g of the inorganic pigment passing a sieve of 325 mesh were dispersed therein. The coating liquid thus obtained was coated onto a 40 g/m.sup.2 paper in a solid content of 5 g/m.sup.2 by means of coating rod and dried to obtain the color developer sheet of the present invention.

COMPARATIVE EXAMPLE 6

20 g of fine powder of a metallic compound of a polymer obtained in the same manner as in Example 6 was dispersed in a solution of 10 g of the binder shown in Table 3, as a solid, dissolved or dispersed in 100 ml of the solvent shown in Table 3. The coating liquid thus obtained was coated onto a 40 g/m.sup.2 paper in a solid content of 4 g/m.sup.2 by means of a coating rod and dried to obtain a color developer sheet for comparison.

Comparative Test Results

The color developing sheets of the present invention and those for comparison, as produced above, were colored by placing them on the above microcapsule sheet and adding a load of 600 kg/cm.sup.2 thereto. After allowing it to stand in the dark for 1 day, a refraction absorption spectrum of colored surface in 700 to 400 m .mu. was measured and the light absorption degree (hereinafter referred to as density) in its maximum absorption was the color density.

The results are shown in the following Table 3. ##SPC2##

In the Examples, "Osmos N" manufactured by Shiroishi Industry Co., Ltd. was used as the colloidal hydrated aluminum silicate; "Georite S" by Sun Georite Kogyo Co., Ltd. as georite, "GT-2" by Bakelite Chemical Mining Co., Ltd. as kaoline, and "NC-earth" by Japanese Talc Industry Co., Ltd. as bentonite.

From the above table, it has been found that the color developer sheet using a metallic compound of a polymer of an aromatic carboxylic acid having at least one hydroxyl group and an aldehyde is more excellent in color developing ability by adding an inorganic pigment thereto.

EXAMPLE 7

138 g of salicylic acid and 325 g of 37% formaldehyde were polymerized by adding 250 g of 12N sulfuric acid as a catalyst thereto and heating at 95.degree. to 97.degree.C for 1 hour. 150 g of the above polymer P-1 was dissolved in 500 ml of warm water in which 40 g of sodium hydroxide was dissolved. After dissolving the water-soluble metallic salt shown in the following Table 4 and dissolved in 500 ml of warm water, it was gradually added thereto under stirring. Next, 50 g of the binder shown in Table 4, dissolved or dispersed in 500 ml of warm water were added thereto. Further, 0.5 mole of the organic carboxylic acid or metallic salt thereof shown in Table 4 was added thereto to obtain a coating composition. The resulting coating composition was coated onto a 40 g/m.sup.2 paper so as to give a solid content of 5 g/m.sup.2 and dried to give a color developer sheet.

COMPARATIVE EXAMPLE 7

The same coating composition as in Example 7 was prepared except an organic carboxylic acid or metallic salt thereof was not used.

This coating composition was coated onto a 40 g/m.sup.2 paper to give a metallic salt of a polymer P-1 of 5 g/m.sup.2 in content and dried to obtain a color developer sheet.

EXAMPLE 8

154 g of 2,6-dihydroxybenzoic acid and 325 g of 37% formaldehyde were polymerized by adding 250 g of 12N sulfuric acid as a catalyst thereto and heating at 95.degree.-97.degree.C for 1 hour. 166 g of the resulting polymer P-2 was dissolved in 500 ml of warm water in which 40 g of sodium hydroxide was dissolved. The water-soluble metallic salt shown in the following Table 4 and dissolved in 500 ml of warm water was added to this solution under stirring. Next, 50 g of the binder shown in Table 4, dissolved or dispersed in 500 ml of warm water, was added thereto. Further, 0.5 g of the organic carboxylic acid or metallic salt thereof shown in Table 4 was added thereto to obtain a coating composition. The coating composition was coated onto a 40 g/m.sup.2 paper to give a metallic salt of polymer P-2 of 5 g/m.sup.2 in content and dried to obtain a color developer sheet.

COMPARATIVE EXAMPLE 8

The same composition was prepared as in Example 8 except that an organic carboxylic acid or metallic salt thereof was not employed.

This coating composition was coated onto a 40 g/m.sup.2 paper to give a metallic salt of a polymer P-2 of 5 g/m.sup.2 in content and dried to obtain a color developer sheet.

Results of Comparative Tests

1. The color developer sheets of the present invention (Examples 7 and 8) and those produced in Comparative Examples 7 and 8 were color developed by piling thereon a paper coated with microcapsules containing crystal violet lactone color former and adding a 600 kg/cm.sup.2 load thereto. After being allowed to stand in the dark for 1 hour, a spectral absorption curve between 700 and 400 m .mu. in wavelength was measured and the color developing ability of the color developer sheets was observed by a density (D.sub.1) at the maximum absorption (wavelength 610 m .mu.).

(2) After measuring the density as described above, the material was exposed to sunlight for 2 hours and the density (D.sub.2) was measured in the same manner as above.

The light fastness value was given from the values of D.sub.1 and D.sub.2 as follows:

Light fastness value (%) = D.sub.2 /D.sub.1 .times. 100

The higher the value is, the better the light fastness of the color images is.

3. The whiteness (W.sub.1) of the untreated surface of the color developer sheet was measured by means of a Hunter's whiteness meter. Next, after being allowed to stand in a room for one month, the whiteness (W.sub.2) of the sample was similarly measured.

The yellowing value was given from the values of W.sub.1 and W.sub.2 as follows:

Yellow value (%) = W.sub.2 /W.sub.1 .times. 100

The higher the value is, the more the yellowing is difficult. ##SPC3##

In the above Table, P-2 shows a polymer of salicylic acid and formaldehyde, and P-2 shows a polymer of 2,6-dihydroxybenzoic acid and formaldehyde.

Thus, by coexisting an organic carboxylic acid or metallic salt thereof, the color developing ability of the color developer sheet was improved and also the light fastness of the colored body and the yellowing of the surface of the color developer sheet were improved. In addition, the film strength of the surface of color developer sheet was increased and the film quality became smooth.

Thus, the pressure sensitive recording paper was more elevated in article value since various properties were improved.

And also, for color formers other than crystal violet lactone the light fastness of the color developer and color images were improved.

EXAMPLE 9

A polymer P-1 was obtained in the same manner as in Example 7. 150 g of the polymer was dissolved in 500 ml of warm water in which 56.1 g of potassium hydroxide was dissolved. This solution was slowly added to 500 ml of warm water in which the water-soluble metallic salt shown in Table 5 was dissolved under stirring. Immediately after addition, a precipitate was produced. After filtering and washing with water several times, it was dried and ground to obtain a fine powder.

Next, after dissolving or dispersing 10 g, in solid content, of the binder shown in Table 5 in 100 ml of the solvent shown in Table 5, 30 g of the fine powder of the metallic compound of the polymer so obtained and 30 g of the aliphatic carboxylic acid or alkaline salt thereof shown in Table 5 were added thereto to obtain a coating composition. This coating composition was coated onto a 40 g/m.sup.2 paper in 4.5 g/m.sup.2 of metallic compound of polymer and dried to obtain a color developer sheet.

COMPARATIVE EXAMPLE 9

The same coating composition was prepared as in Example 9 except that an organic carboxylic acid or metallic compound thereof was not employed.

This coating composition was coated onto a 40 g/m.sup.2 paper in 5 g/m.sup.2 of metallic compound of polymer and dried to obtain a color developer sheet.

Comparative Test Results

A test was conducted as in the previous Comparative Tests. The results are as shown in the following Table 5. ##SPC4##

EXAMPLE 10

A polymer was obtained in the same manner as in Example 7, and 150 g of the polymer was dissolved in 500 ml of warm water in which 56.1 g of potassium hydroxide was dissolved. 144 g of zinc sulfate dissolved in 500 ml of warm water was slowly added thereto and simultaneously a precipitate was produced. After filtering and washing with water several times, it was dried and ground to obtain a fine powder.

30 g of the fine powder obtained by the above method was dispersed in ethanol and 10 g of ethylcellulose was dissolved therein to obtain a coating composition. The composition was coated onto a 40 g/m.sup.2 paper, with a dry content of metallic compound of polymer of 45 g/m.sup.2 and dried. Next, stearic acid dissolved in ethanol was coated onto the coated paper in a solid content of 2 g/m.sup.2 and dried.

COMPARATIVE EXAMPLE 10

The same coating composition prepared as in Example 10, except that stearic acid dissolved in ethanol was not employed, was coated onto a 40 g/m.sup.2 paper in a metallic compound of polymer content of 5 g/m.sup.2 and dried to obtain a color developer sheet.

Comparative Test Results

Tests were conducted as in the former Comparative tests. The results are as shown in the following Table 6.

TABLE 6

Color Density Light Fastness of Crystal of Violet Color Images Yellowing Lactone (D.sub.1) (%) Degree (%) Example 10 0.704 72 58 Comparative Example 10 0.641 63 50

The present color developer sheets were further improved in color developing ability, and light fastness of the color images against sunlight irradiation as well as yellowing in comparision with conventional sheets. In addition, the film strength was increased and the film quality became smooth.

For color formers other than crystal violet lactone, the color developing ability was similarly improved and the light fastness of the colored images was improved.

Claims

What is claimed is:

1. A recording sheet comprising, in combination with a color former which comprises a colorless dye-forming organic compound, a support having coated thereon a layer of color developer comprising a metal compound of a polymer, said polymer, having at least one hydroxyl group and being a reaction product of an aromatic carboxylic acid with an aldehyde or acetylene, and said metal being selected from the group consisting of Groups Ib, IIa, IIb, IIIa, IVa, IVb, VIIb and VIII of the Periodic Table, said color developer being capable of forming a distinct color when contacted with said color former.

2. The recording sheet of claim 1 wherein said polymer is a salicylic acid-aldehyde polymer, a p-hydroxybenzoic acid-aldehyde polymer, a 2,6-dihydroxy-benzoic acid-aldehyde polymer or a salicylic acid-acetylene polymer.

3. The recording sheet of claim 1 wherein said color developer further contains an inorganic pigment.

4. The recording sheet of claim 1 wherein said color developer further contains an organic carboxylic acid or a metal compound thereof.

5. The recording sheet of claim 1 wherein said metal is selected from the group consisting of copper and silver.

6. The recording sheet of claim 1 wherein said metal is selected from the group consisting of magnesium and calcium.

7. The recording sheet of claim 1 wherein said metal is selected from the group consisting of zinc, cadmium and mercury.

8. The recording sheet of claim 1 wherein said metal is selected from the group consisting of aluminum and gallium.

9. The recording sheet of claim 1 wherein said metal is selected from the group consisting of tin and lead.

10. The recording sheet of claim 1 wherein said metal is selected from the group consisting of chromium and molybdenum.

11. The recording sheet of claim 1 wherein said metal is manganese.

12. The recording sheet of claim 1 wherein said metal is selected from the group consisting of chromium and nickel.

13. The recording sheet of claim 1 wherein said metal is selected from the group consisting of zinc, tin, aluminum and nickel.

14. The recording sheet of claim 1 wherein said metal compound of said polymer is prepared by reacting an alkali metal salt of said polymer with an inorganic acid or organic acid salt of said metal.

15. The recording sheet of claim 1 wherein said color former is coated onto the same side of said support as said layer of said color developer.

16. The recording sheet of claim 1 wherein said color former is coated onto the opposite side of said support from said layer of said color developer.

17. The recording sheet of claim 1 wherein said color former is coated onto a second support different from the support having coated thereon said layer of said color developer.

18. The recording sheet of claim 3 wherein said inorganic pigment is present in an amount of greater than 1 part by weight based on 100 parts by weight of said metal compound of said polymer.

19. The recording sheet of claim 18 wherein said inorganic pigment is present in an amount of from 10 to 1000 parts by weight based on 100 parts by weight of said metal compound of said polymer.

20. The recording sheet of claim 1 wherein said layer of said color developer comprises said metal compound of said polymer dispersed in a binder therefor.

21. The recording sheet of claim 1 wherein said layer of said color developer is coated onto said support in an amount of greater than 0.1 gram per square meter of said support.

22. The recording sheet of claim 21 wherein said layer of said color developer is coated onto said support in an amount of from 0.5 to 5 grams per square meter of said support.

23. The recording sheet of claim 4 wherein said organic carboxylic acid has at least 6 carbon atoms and wherein said metal compound thereof comprises a metallic salt thereof, said metal being selected from the group consisting of sodium, lithium, potassium, magnesium, calcium, zinc, cadmium, aluminum, tin, lead, chromium, manganese, cobalt, and nickel.

24. The recording sheet of claim 23 wherein said organic carboxylic acid or said metal compound thereof is present in an amount of greater than 10 parts by weight based on 100 parts by weight of said color developer.

25. The recording sheet of claim 24 wherein said organic carboxylic acid or said metal compound thereof is present in an amount of from 20 to 200 parts by weight based on 100 parts by weight of said color developer.