CA1099099A - Recording sheet and color developer therefor - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A recording sheet comprising a support having coated thereon a color developer layer containing a metallic compound of aromatic carboxylic acid as a color developer capable of forming a distinct color when contacted with a color former.

Description

l~q~9 1 The present invention relates to a recordiny sheet an~
a color developer therefor, and more particularly to a recording sheet having coated thereon novel color developer layer and a novel color developer for the recording sheet.
There have been known recording sheets utilizing a color reaction of a colorless organic compound (hereinafter, referred to "color former") and an adsorbent material capable of forming a distinct color when contacted with the color former.

As the recording sheets using the phenomenon, a pressure-sensitive recording sheet (USP 2,505,470, USP 2,505,489, USP

2,550,471, USP 2,548,366, USP 2,712,507, USP 2,730,456,USP 2,730,457, USP 3,418,250, etc.) and a heat-sensitive recording sheet have been well known. Further, it has been known a printing method, that an ink containing the color former is applied to the color developer sheet through a medium such as 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 paraffine or other organic solvent. The solution may be dispersed in a binder and/or may be microencapsulated, and then coated on a support such as paper, plastic film, resin-coated paper, etc.
In case of heat-sensitive recording sheet, the color former may be coated on the support together with a thermofusible material such as acetoanilide 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 ,~

l~q~9 such as styrene-butadiene rubDer latex a~d then coated on or impregnated into a base support before or directly before recording.
The color former and color developer may be coated on the same surface or opposite surfaces of support, or the different supports.
Usually, after the color developer is coated on the support, a desensitizer is locally coated thereon in order that unnecessary surface portion is prevented from the color formation .10 (USP 2,777,780). Another embodiment of the prevention of color formation is to locally coat the color developer on the support or the coated layer of color former without using the desensiti-zer.
As the above described color developer, there are clays such as acid clay, active clay,attapulgite, zeolite, bentonite, etc., phenol resins (USP 3,516,845i USP 3,540,911) and organic compounds such as succinic acid, tannic acid, gallic acid or phenol compound (USP 3,244,548) are known. Such organic compound is not practically employed for the reason that the color developing ability of 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 case where the above color developer is locally coated on a support to form a color developer sheet, if large amount thereof (7-10 g per 1 m2 of the support) is coated, the color developer sheet cannot form sufficient color when contacted with the color former. As the result, locai _30 coating method is limited.

1~19~99 1 In this case, since locally coated portion of the color developer sheet is thicker than the other portion, the color former coated on another support, when contacted with the color developer sheet, is locally pressurized to form unpreferable color (herein-after, referred to "fog").
The inventors have found that all defects of the color developer sheet and ink can be completely removed by using a metallic compound of an aromatic carboxylic acid. That is,the in-ventors have found that the color developer composed of a metallic compound of an aromatic carboxylic acid is far stronger in color developing ability than aromatic carboxylic acid or metallic com-pound, and that the color formed on the color former sheet is stronger in light resistance.
The metal compound of aromatic carboxylic acid used in the color developer of the invention can be prepared by reacting an alkali metal salt of aromatic carboxylic acid and a water-soluble metal salt in a solvent in which both are soluble. In this case, the ratio of the alkali metal salt and water-soluble metal salt is not particularly limited, but a molar ratio of 1 : 1 is preferable.

The alkali metal salt of aromatic carboxylic acid used in the above reaction can be prepared by conventional synthetic methods. For example, it may be prepared by reacting an aromatic carboxylic acid with an alkali metal hydroxide or carbonate.
The aromatic carboxylic acid used in the present invention includes, for example, benzoic acid, o-nitrobenzoic acid, m-nitro benzoic acid, p-nitrobenzoic acid, o-chlorobenzoic acid, m-chloro-benzoic acid, p-chlorobenzoic acid, o-toluic acid, m-toluic acid, p-toluic acid, o-bromobenzoic acid, m-bromobenzoic acid, p-bromo-benzoic acid, o-iodo-benzoic acid, m-iodobenzoic acid, p-iodobenzoic acid, 4-methyl-3-nitrobenzoic acid, 2-chloro-4-nitrobenzoic acid, _30 2,3-dichlorobenzoic acid, 2~4-dichlorobenzoic 1~99~99 1 acid, p-isopropylbenzoic 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-di-tert-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-hydroxy-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-dihydroxybenzoic acid, 2,5-dihydroxybenzoic acid, 2,6-dihydroxybenzoic acid, l-naphthoic acid, 2-naphthoic acid, 1-hydroxyl-2-naphthoic acid, 2-hydroxyl-

3-naphthoic acid, 2-hydroxyl-1-naphthoic acid, 5,5'-methylene-salicylic acid, thiosalicylic acid, trimellitic anhydride, anacardic acid, benzoic anhydride, 2-carboxybenzaldehyde, diphenic acid, etc. Above all, aromatic carboxylic acid having at least one hydroxyl group in the structure, especially ortho position, are effective.
As metals of metal salts to be reacted with alkali metal salts of carboxylic acids, there are the group Ib metals such as copper, silver, etc., the group IIa metals such as magnesium, calcium, etc., the group Ilb metals such as zinc, cadmium, mercury, etc., the group IIIb metals such as aluminum, gallium, etc., the group IVb metals such as tin, lead, etc., the group VIa metals such as chromium, molybdenum, etc., the group VIIa metals such as manganese, etc., the group VIII metals such as _30 cobalt, nickel, etc., and the like. Among these, those wherein zinc, tin~aluminum or nickel is used, are especially effective.
In using them in the reaction, t~ey are used in the form of inorganic salt thereof such as chloride, sulfate, nitrate, etc., or in the lorm of organic salt thereof such as oxalate, acetate, etc. These Metal salts or alkali metal salts of the aromatic ca-~boxylic acid exhibit almost no color-developing ability when used separately, but, when these reaction products is coated on,o a support, metal salts of carboxylic acids show the following excellent color-developing ability.
.10 The metal salt of the aromatic carboxylic acid which is prepared by the reaction between the alkali metal salt of the aromatic carboxylic acid and a water-soluble metal salt may be used as the reaction mixture or, more preferably, after the separation and the purification.
Further, for the purposes of increasing color developing ability and light resistance, an inorganic pigment may be added to the color developer. The inorganic pigment contains aluminum silicate, zinc silicate, lead silicate, tin silicate, colloidal hydrated aluminum silicate, zeolite, bentonite, kaolinite active clay, acid clay, talc and the like. An amount of inorganic pigment has no critical value, for example, more than 1 part by weight, preferably S parts by weight per 100 parts by weight of the metal compound of the aromatic carboxylic acid.
The color developer of the invention can be prepared by dissolving or dispersing the metal compound of aromatic carboxylic acid in water or an organic solvent such as methanol, ethanol, butanol, ethyl acetate, butyl acetate, benzene, toluene acetone, tetrahydrofuran or methylene chloride. Water and organic solvent may be mixed. Preferable solvent is capable of dissolving the _30 organic carboxylic acid. In case of adding the inorganic pigment, i it may be dispersed in water, the organic solvent, the solution or the dispersion. A concentration can be decided according to the conventional manner.
Thus prepared solution or dispersion can be coated on a support, if necessary, together with a binder such as gum arabic, ethyl cellulose, styrene-butadiene copolymer, nitro-cellulose, styrene-butadiene latex, methylmethacrylate-butadiene latex, etc. An amount of the binder can be easily decided by one skilled in the art. It should be noted that the coated layer .10 of color developer can be maintained on the support even if the binder is not present in the layer.
An amount of the color developer coating composition is not specifically limited to obtain sufficient color. For example, it is more than 0.1 g/m2, preferably 0.5 - 5 g/m2. The upper limit of coating amount is not limited in a point of color developing activity, and the above range is only due to economical reason.
The color developer composition on a support can be coated on a support by all kinds of coating method because the present .20 invention is basically characterized by using the metallic compound of the aromatic carboxylic acid.
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 aromatic carboxylic acid is dissolved or dispersed in the resulting solution.
The plasticizer may contain esters of phosphoric acid, phthalic acid, adipic acid or sebatic acid (e.g. tributyl phos-phate, dibutyl phthalate, dioctyl phthalate, butyl adipate, dibutyl sebacate): hydrocarbon such as chlorinated paraffin; and g 1 glycerine of unsaturated fatty acid such as castor oil.
In this case, for the purpose of stabiliziny the color developer composition which rnay be used as a coatiny ink, an alkali metal salt of organic acid, or an alkali may be added to the composition. The alkali metal salt of organic acid is, for example, lithium salt, sodium salt or potassium salt or butyric acid, caprylic acid, palmitic acid, oleic acid, linoleic acid, linolenic acid, benzoic acid, and the like. The alkali are, for example, sodium hydroxide, potassium hydroxide, sodium .lO carbonate, sodium silicate, borax and conventional alkali compound. An amount of the alkali is 0.01 - 1 parts by weight per 1 part by weight of metal compound of aromatic carboxylic acid.
Each component is dissolved or dispersed by means of ball mill or sand mill. Thus prepared color developer ink can be locally applied to a support.
A color developer sheet and color developer of the invention can be used in combination with conventional color former such as crystal violet lactone, benzoyl leuco methylene blue, malachite green lactone, rhodamine B lactam, fluoranes (USP 3,501,331; USP 3,514,310; USP 3,514,311; USP 3,540,911), spiropyrans (USP 3,293,060), a mixture thereof and the like~
The modification of the invention can be easily carried out by one skilled in the art in accordance with conventional information, technique and the like.
The color formers for pressure-sensitive copying pa-per are ordinarily employed in combination in order to secure the instantaneous color forming property and light fastness of colored image. For example, a combination of instantaneous _30 color forming crystal violet, lactone or 3-methyl-2,2'-spirobi ~benzo(f)]-chromene as a ~rimary color former and benzoyl leucomethylene blue having an excellent liyht fastness has been most well known, however, the colored image obtained by contacting the 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 or chromene 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 aromatic carboxylie acid and crystal violet lactone or chromene 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 erystal violet laetone in the below deseribed Examples.
Comparing with the eonventional clay-coated paper, the color developer sheet of the present invention has the following advantages:
The conventional clay-coated paper tends to be decreased in sensitivity of elay, when being allowed to stand in air, .20 beeause of adsorbing materials in air on the aetive point of elay. That is, the eolor developing ability of eolor developer sheet is remarkably lowered with time.
In the eolor developer sheet of the present invention, sueh defeet has been improved. And, in ease of manufaeturing a eolor developer sheet in aeeordanee with the present invention, suffieient eolor developing ability and other properties necessary to the eolor developer sheet for pressure sensitive paper ean be satisfied with smaller eoating amount than in the eonventional elay paper. That is, the amount of eolor developer of the present invention to be eoated is suffieient with 0.1 to 5 g/m2 ~ Q ~$ ~ 9 1 while in the conventional clay paper the amount to be coated is 7 to 10 g/m2. Thus, the color developer sheet is possible to make a size spray coating by means a machine from that it can do with a small amount and that the physical properties of liquid can be freely varied different from clay, and results in a remarkable effect not only on performance but also on production.
Furthermore, the color developer of the present invention can give the similar color developing ability with smaller amount (about 2 g/m ) of it to be coated if a natural or synthetic high molecular substance or a water repellant is previously coated on the surface of paper.
The present invention will be 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.
Microcapsules containing a color former is manufactured, for example, according to the specification of U.S. Patent No. 2,800,457, as follows:

10 parts by weight of acid-treated pig skin gelatin and 10 parts by weight of gum arabic were dissolved in 400 parts by weight of water at 40C and 0.2 part 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~ of crystal violet lactone or 3-dibenzylamino-7-diethylaminofluorane dissolved in an oil con-sisting of 4 parts by weight of chlorinated diphenyl and 1 part by weight of kerosene. The emulsification was stopped when the size of oil droplet became to 5 microns on an average. Water at 40C was added thereto to 900 parts by weight in total and the _30 stirring was continued. At this time attention must be paid ~ Q 9~

1 so that the liquid temperature does not lower to below 40C.
Next, 10% acetic acid was added thereto to adjust the pH of 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 to 20C, 7 parts by weight of 37% formaldehyde were added thereto and at 10C, 10% aqueous solution of caustic soda was added to ad]ust the pH to 9. At this time, addition of caustic soda must be carried -10 out with sufficient attention.

The liquid temperature was raised to 50C by heat under stirring for 20 minutes. The microcapsule thus obtained was controlled to 30C and thereafter was coated on 40 g/m2 paper - in 6 g/m2 as solid content and dried. Also in case of other color former the recording paper was manufactured in the same manner as described above.
The alkali metal salt of aromatic carboxylic acid used for the production of the developing sheet of the invention is prepared by reacting an aromatic carboxylic acid with an alkali metal hydroxide or carbonate. An example of the procedure is as follows: 30 g of sodium hydroxide is dissolved in 300 ml of water, to which 100 g of salicylic -acid is then added with agitation. The agitation is continued for a while to dissolve the salicylic acid completely and then the solution is evaporated to dryness to obtain 110 g of sodium salicylate.
Sodium salts and potassium salts of aromatic carboxylic acid may similarly be prepared to that mentioned above.

The following examples are to illustrate the invention in more detail without limiting the same.
_30 1 Example 1 0.69 g equivalent of the sodium salt of aromatic carboxylic acid obtained by the above mentioned procedure was dissolved in 150 ml of warm water. On the other hand, 0.6 g equivalent of the sulfate was dissolved in 150 ml of warm water and added to the above mentioned aqueous solution of sodium aromatic carboxylate with agitation. After a while, the metal compound of aromatic carboxylic acid was precipitated. It was then filtered and washed with water several times to obtain the same.
10 g of the following binder was then dissolved in 300 ml of the solvent, in which 70 g of the resulting aromatic carboxylic acid and 30 g of the inorganic pigment were dispersed or dissolved. The so obtained solution was applied to an original paper of 50 g/m2 to give a coating of 3 g/m2 by means of a coating rod, followed by drying.
Example 2 0.1 g equivalent of the sodium salt of aromatic carboxylic acid obtained by the above mentioned procedure and 10 g of gum arabic were dissolved in 150 ml of water. On the other hand, 0.1 g equivalent of the water-soluble metal salt was dissolved in 150 ml of warm water and added thereto with agitation.
When the stirring was continued for a while, fine crystals deposited. 50 g of the following inorganic pigment was dis-persed in the resulting dispersion and applied to an original paper of 50 g/m2 to give a coating of 4 g/m2 by means of a coating rod folloWed by drying.
Comparative Example 1 7 g of the binder was dissolved in 300 ml of the solvent, in which 70 g of the aromatic carboxylic acid was dispersed.

~ The resulting dispersion was applied to an original paper of 1~9~9 '.

1 50 g/m2 to give a coating of 2.1 y/m2 by means of a coating rod followed by drying.
Comparative Example 2 0.1 g equivalent of the sodium salt of aromatic carboxylic acid and 7 g of gum arabic were dissolved in 150 ml of warm water, to which 0.1 g equivalent of the water-soluble metal salt dissolved in 150 ml of warm water was added with stirring. When the stirring was continued for a while, fine crystals deposited.
The resulting dispersion was applied to an original paper of 50 g/m2 to give a coating of 3 g~m2 by means of a coating rod, followed by drying.
Comparative Test 1 On the developing sheets of Examples 1 and 2, and Com-parative Examples 1 and 2 were contacted with microcapsule sheets containing crystal violet lactone and pressurized under a load of 600 kg/cm2. After allowed to stand in the dark for a day and night, the reflective absorption spectrum at 400 - 700 m~ was measured, the extinction factor at its absorption maximum (which will hereinafter be referred to as "density") being defined as "fresh density". After further exposed to the sunlight for 1 : 2 hours, the reflective absorption spectrum on the developed surface was measured to give its density. From the foregoing results, a value of light resistance defined by the following relation was obtained.

Density of color images after exposed to sunlight Light resistance (%) = 2~ 100 Fresh density of color images These results are shown in Table 1.

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~ ~ o~ ~ ~ ~ o~ o ~` o '~1 O N ~100 CO C5'~ 0~ ~ ~ ~ r~
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O

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rl > .,1 X ~, O ~ U = = = , =
~ Id U ~I rl .¢ u ~ ~a u ~ ~d a o .
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X

30 z ~L~99~9 ~--~D O O ~ ~ ~ O ~ o U~ t~ ~ U~ O ~ O
.
~ ~ 1~ r~ ~) O ~ u~ N C~l 10 r` ~ O

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= ~ V = ~ ~ =
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x ~ o.,l v ~V I o I o I ~ Io Io I o 1.
N I rl I I I U a ~q I XI ~ I X

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~ u~ V ul ~ V ~ N u~ N V 'I ~ ~

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_30 ,~Q~99 Comparative Test 2 The similar tests to Comparative Test 1 were carried out using a microcapsule sheet containing 3-dibenzylamino-7-diethyl-aminofluoran to obtain the results as shown in Table 2.

No. Example Aromatic Water- Inor- Sol- Binder Fresh Light re-or Com- carboxy- soluble ganicvent den sistance parative lic acid metal pigment sity after ex-Example salt posed for 1 1 sali- zinc colloi-etha- ethyl 0.66 86.5 cylic sulfate dal alu- nol cellu-acid minum lose silicate hydrate ~ " 0.50 73.6 2 " ~ tir, zeolite etha- " 0.72 77.5 sulfate nol:

.l l _ __ 1~ ~ 0.45 51.5 3 " " tin bento- etha- " 0 61 82.0 sulfate nite nol Il ll ____ ll " 0.53 52.0

4 silicate " 0.63 84.0 " " " kaolin " " 0.65 78.5 6 " " " zinc oxide" " 0.64 79.5 7 calcium ben- 71.2 carbonate zene " " ---- " " 0.51 42.3 3~

~ ' 1 8 2 sali- manga- colloi- water gum 0.34 82.0 cylic nese ~al alu-- arabic acid sulfate minum silicate hydrate ~ " 0.23 60.0 9 `' " cobalt zinc " pol sulfate oxide vinyl 0.32 97.2 alcohol ~ " 0.24 85.0 10 " ~ sulfate licate arabic " " ---- " " 0.36 96.0 ,1 0 11 " " lead kaolin " " 0.35 30.3 sulfate " " ---- " " 0.23 23.5 12 " ~ copper kaOlin 0.45 52.6 sulfate " ., ____ ~ " 0.30 43.0 13 " benzoiczinc colloi- 0.32 31.5 acid sulfate minum si-licate hydrate " " ---- " " 0.28 22.0 14 " o-chloro-zinc kaolin " " 0.46 32.0 benzoicchloride acid ~20 " " ~ 0.30 22.6 " 2-hydroXY- alUmi~ kaolin butyl nitro-l-naphthoic num ace~ate cellu-0.48 47.0 acid chloride lose " " ____ " ~ 0.37 32.6 16 " 2-hydroxy- i k 1 kaolin lose " ~ ' " 0.35 89.0 .
Com arative Test 3 p The similar tests to Comparative Test 1 were carried out using a microcapsule sheet containing 3-methyl-2,2'-spirobi[benzo(f)]
c'nromene as a color former to obtain the results as mentioned in ~9~1~99 1 in Table 3.
TAsL~ 3 No. Example Aromatic Water- Inor- Sol- Binder F-resh Light re-or Com- carboxy- soluble ganic ven~ den- sistance parative lic acid metal pigment sity after ex-Example salt posed for v _ 2 hrs (~) 1 1 salicy- zinc colloi- etha- ethyl lic sulfate dal alu- nol cellu- 0.71 76.1 acid minum lose silicate 1, 1, hydrate 1, ll 0.53 vanished 2 " " tin zeolite ethanol:
sulfate 3 1 0.41 47.5 " " ---- " " 0.32 vanished 3 " " " bento- etha-nite nol " 0.51 41.6 ---- " " 0.34 vanished 4 " . " zinc ll " 0.45 38.5 sillcate " " " kaolin " " 0.60 52.6 6 " " colloi- ll " 0.72 108.5 dal alu-minum si-licate hydrate In the case of using the developing sheet of No. 6, exposure to the sunlight was further carried out for 10 hours to obtain a light resistance of 81.0%.
As is evident from Tables 1 to 3, the developing sheet of the invention exhibits, when stacked on a color former-containing microcapsule sheet and pressed, more excellent developing capacity than when a metal compound of aromatic carboxylic acid alone is used, and its developed color matter has a sufficient light resistance. Similar results were obtained regarding other color formers.
_30 ~C~ ~ 9~ ~3g 1 Example 3 0.6 g equivalent of potassium salicylate prepared by the method above mentioned was dissolved in 150 ml of warm water to prepare aqueous potassium salicylate solution. 0.6 g equivalent of zinc sulfate was dissolved in 150 ml of warm water, then added to the aqueous sodium salicylate solution under stirring.
Immediately, white crystals were separated out. The resulting crystals were filtrated out and washed several times with water to obtain 90 g of white solid. 1 g of ethyl cellulose was -~ dissolved in 200 ml of the solvent and to this solution, was added 50 g of the previously prepared white solid to dissolve.
The resulting solution was coated onto a base paper of 50 g/m2 so that the solid ingredient thereof was coated at the thickness of 3 g/m2, then dried.
Example 4 0.3 gram-equivalent of the sodium salt of the aromatic carboxylic acid obtained in Example 3 and 10 g of the binder was dissolved in 150 ml of warm water, then 0.3 gram-equivalent of the metal salt dissolved in 150 ml of warm water was added .20 thereto under stirring. After stirring for a while, the liquid became emulsified due to the formation of fine crystals. This solution wherein said crystals were dispersed, was coated onto a base paper of 50 g/m2 with coating rod so that the solid ingredient was coated at the thickness of 4 g/m2.
Comparative test 4 Microcapsule sheet containing crystal violet lactone was superposed on the color developer sheet prepared by Examples 3 and 4 and pressurized under the load pressure of 600 I~g/cm2.
Af-cer leaving the sheet for a day in dark, the absorption spectrum of the color images in the visible region was measured, ~Q g~ g t and the absorbance (hereinafter referred to as "density") at the maximum absorption was defined as "fresh density".
In addition, after the irradiation with sunlight for 1 hour, the absorption spectrum of the color images surface in the visible region was measured to determine its density. From the above result, the light resistance value was determined. The results thereof are shown in Table 4. The light resistance value is defined by the following formula;

The density of colored images Light resistance after the irradiation with sunlight x 100 value (%) Fresh density of colored images No. Exam- Aromatic Metal Solvent Binder Fresh Light resis-ple carboxy- Salt density tance value lic acid after the irradlation with sun-light for 1 hour .
1 3 Salicylic Zinc SulEthanol Ethyl 1 07 91.5 2 " Ethanol lose :water .20 (3:1) " 0.95 85.5 3 4 nesge sul- arabic 0.56 75.9 fate Water " " Cobalt Water " 0.68 67.5 sulfate " Tin sul~ Water 0.86 79-3 fate 6 " Nickel Water 0.82 84.8 sulfate 7 ll - ChrmiUm Water " 0.64 97.8 8 " Lead Water " 0.39 51.0 sulfate " cOPPer Water 0.70 66.7 sulfate _3G 10 " Benzoic Zinc Water " 0.61 63.0 acid sulfate 11 4 o-Chloro Zinc Water Gum 0.64 56.0 benzoic sulfate arabic acid 12 " 2-Hydroxy-l-naphth- Zlnc Water " 0.89 73.5 oic acid chlorlde 13 " ' Tin Water 1.10 80.0 chlorlde 14 " ' Nickel Water " 0.83 95,0 15 " 2-HydrXY~ Aluminum 3-naphth- sulfate " 0.81 67.9 16 " Salicylic .10 acid " Water " 0-77 72.0 17 " 2-Hydroxy- Manga-3-naphthoic nese Water " 0.63 94.5 acid sulfate 18 " 5-tert-butyl z nc polyvinyl 1 12 90 3 salicylic chloride alcohol acid 19 " 3,5-di- I~ Water " 0.95 85.2 tert-butyl salicylic acid " 3-phenyl " Water " 0.90 69.5 salicylic acid 21 " 3-methyl-5- " WaterStyrene- 0.94 76.8 tert-butyl butadiene salicylic latex acid 22 " 5-cyclo- " Water " 0.97 74.9 hexyl sali-cylic- acid 23 " 3,5-di- " Water " 0.89 71.4 tert-amyl salicylic acid 24 3 3-methyl- " Ethanol Ethyl 0.93 72.3

5-isoamyl cellu-salicylic lose acid " 5-isoamyl " Methyl " 0.92 71.1 salicylic isobutyl acid ketone _30 _ 20 -~o~

26 3 S-tert- Tin ~5ethanol Ethyl 0.91 67.7 butyl sulfate cellu-salicylic lose acid 27 " 5-tert- Nickel Methanol Ethyl 0.91 71.7 butyl sulfate cellu-salicylic lose acid 28 " 3,5-di- Zinc Acetone " 0.92 70.5 tert-butyl sulfate salicylic acid 29 " 3-cyclohexyl salicylic Copper n-butyl- " 0.71 69.2 acid sulfate acetate 30 " 3-phenyl Mangane- benzene 0.60 61.2 saliCYlic se sul-acid fate 31 " 3,5-di Zinc toluene " 0.91 59.6 sec-butyl sulfate salicylic acid 32 " 5-nonyl- Zinc benzene " 0.90 71.3 salicylic: chlOride acid Comparative test 5 The test described in the above color-developing test 3 was carried out using microcapsule-coated sheet containing 3-dibenzyl-amino-7-dimethylaminofluoran. The results are shown in Table 5.

_30 -- 21 ~

1 TAsLE 5 No. IExam~ Aroma- IMetal saltl Solventl Binder¦ Fresh Light re-ple I tic I I I I densi- sistance carbo- I I i ty value after xylic ~ i l the irra-I acid I l diation with sun-i light for , 1 hour . . j 1 3 Salicylic Zinc Ethanol Ethyl ¦0.75 86.8 acid sulfate cellu- !
lose 2 ., ., " ¦Ethanol ll 0.60 82.5 ~10 I:water (3:1) 3 4 ll Manganese Water Gum 0.45 80.0 sulfate arabic 4 " .. Cobalt .. .- 0.48 92.5 sulfate ~- .. Tin .- .. 0.80 70.5 . sulfate

6 ~. .- Nickel .- .. 0.79 90.5 sulfate

7 ., .- Chromium .. .. 0.72 98.0 sulfate .20 . .

8 .. .. Lead .. .- 0.44 51.3 sulfate _ . .

9 ., .- Copper .. .. 0.61 71.5 sulfate . . , ¦10 ., Benzoic Zinc - .. 0.56 50.2 i acid sulfate . .
~11 .- o-Chloro- .. .- .. 0.59 j 54.5 benzoic acid - ! ~
12 I" 2-llydroxy- Zinc ,- - 0.73 ~i 79.4 i l-naphth- chloride ' oic acid _30 , . i ~L~g9~9 1 13 , 4 1 2-llydroxy-l Tin ~ jO-81 79.0 i ! l-naphth- Ichloride , i I I oic acid ¦
! ~ . ¦
14 ! ~ I Nickel ~ " ¦ " 0.70 94.5 , ¦ sulfate `
; l i 15 ,l 2-Hydroxy- Aluminum I
3-naphth- sulfate j " ll0.67 66.2 oic acid _ .
16 ll Salicylic ll ll ll 0.73 67.5 _ ~
17 ll 2-Hydroxy- Manganese ll ll 0.57 92.3 3-naphth- sulfate .10 oie aeid _ I
18 4 5-tert- Zine Water polyVinYlo 7672.4 butyl sali- ehloride aleohol .
eylie aeid _ I
19 ll 3,5-di-tert- ,l ll ll 0.7568.3 butyl sall, eylie aeid . _ ll 3-phenyl ll ll .l 0.6567.2 salieylie aeid 21 ll 3-methyl- ll ll Styrene- 0.78 70.2 5-tert- butadi-salieylie ene late~
.20 aeid . _ 22 'l hexyellO- ,l ., 'l 0.7g68.8 aeid _ _ .
23 ll 3,5-di- ll ,. . 0.7366.3 tert-amyl salieylie acid 24 3 3-methyl- " Ethanol Ethyl 0.76~ 70.0 5-isoamyl eellu-salieylie lose _ ~l I

1 25 .l 5-isoamyl 1 Methyl .l 0.75¦ 68.1 _30 ~ salieylie iso-aeid butyl ketone 1~99~9 1 26, 3 i 5-tert~ ; Tin MethanoII Ethyl 0.73 65.6 . butyl sulfate ¦ cellu-salicylic ¦ lose ,1 .
27l ll Nickel ~ sulfate ll ll 0.62 66.9 I
28 'l butyl Zsulnfcate Acetone 'l 0.70 67.1 salicylic _ 29 ll 3-cyclo- Copper n-butyl- ll 0.61 6S.5 salicylic sulfate acetate . .
3 3-phenyl Manganes~ Benzene Ethyl 0.51 58.0 salicylic sulfate cellu-31 .. 3,5-di-'. 7.inc sec-butyl.- sulfate Toluene ll 0.71 56.3 sa~cylic aclu 32 ll 5-nonyl- Zinc Benzene ll 0.61 62.0 L ~ ~licy:ic cblcr ~
.

.20 It can be understood from Tables 4 and 5 that, when contacted with a color-former-containing capsule sheet under pressure, the color developer sheet of this invention shows sufficient color density and the light resistance of the color image formed.
In addition, the color image formed on the color developer sheet has resistance to the "wetting with water". Especially, when 2-hydroxy-1-naphthoic acid, 2-hydroxy-3-naphthoic acid, etc.
are used, the color image formed did not disappear at all when wetted with water.
~30 Similar results were obtained about the other color formers.

~9~9 1 Example S
100 parts by weight (hereinafter, "part" means l'part by weight") of potassium salicylate prepared in the above-described manner was dissolved in 150 parts of hot water, and into the solution was added with stirring 60 parts of stannous chloride dissolved in 150 parts of hot water, whereby stannous salicylate was immediately precipitated as white crystals. The crystals were filtered out, washed several times with water, and then dried to obtain 100 parts of stannous salicylate as solids.
40 parts of nitrocellulose was dissolved in a mixture of lS parts of butyl acetate, 80 parts of isopropanol and 60 parts of butanol to give a homogeneous solution, into which 120 parts of above-described solid stannous salicylate was mixed and totally dissolved or dispersed by a ball mill to obtain a developer ink as a white suspension. The ink was diluted with a 1: 1 mixture of ethyl acetate and ethanol to give a viscosity of about 0.7 poises and printed by a flexographic printing process to give 3 g/m2 of dried coating film.

Example 6 .20 100 parts of sodium 2-hydroxy-3-naphthoic acid was dissolved into lS0 parts of hot water and into the solution was added with stirring 40 parts of zinc chloride dissolved in 150 parts of water, whereby zinc 2-hydroxy-3-naphthoate was immediately precipitated as crystals. The resulting mixture was concentrated to a total weight of 200 parts. Into a mixture of 15 parts of dioctyl phthalate, 120 parts of ethyl acetate, 100 parts of isopropanol and 80 parts of methanol was dissolved 50 parts of et'nyl cellulose to give a homogeneous solution to which were added 200 parts of the above-described concentrate and 50 parts -30 of kaolin and completely dissolved or dispersed in a ball mill to lQ99~99 1 obtain a developing ink in the form of a suspension. The ink was diluted with a 1 : 1 mixture of ethyl acetate and ethanol to give a viscosity of about 0.7 poise and printed by a flexo-graphic printing process to give 3 g/m2 of dried coating film.

Exam le 7 p 100 parts of sodium o-chlorobenzoic acid obtained by the aforementioned method was dissolved in 150 parts of hot water and into the solution was added with stirring a solution of 100 parts of nickel sulfate in 150 parts of hot water, whereby crystals of nickel o-chlorobenzoic acid were immediately preci-pitated, the precipitate filtered out, washed several times with water and dried to obtain 80 parts of solid nickel o-chlorobenzoic acid~ Into a mixture of butyl adipate, ethyl acetate, 20 parts of methyl ethyl ketone and toluol was dissolved 8 parts of vinyl chloride-vinyl acetate copolymer to obtain a homogeneous solution into which 20 parts of the above-described nickel o-chlorobenzoic acid and 10 parts of aluminum silicate hydrate (Trade Mark, "Osmos N", manufactured by Shiraishi Kogyo) were mixed followed by homogeneous dissolution or dispersion in a ball mill to obtain .20 a developer ink. The ink was diluted with toluene to give a viscosity of about 1 poise and subjected to a gravure printing process to give 3 g/m2 of dried coating film.
Example 8 100 parts of sodium 2-hydroxy-1-naphthoate prepared by the above method was dissolved in 150 parts of warm water ar.d into the solution was added with stirring a solution of 60 parts of aluminum sulfate in 150 parts of warm water whereby crystals of aluminum 2-hydroxy-1-naphthoate were immediately precipitated.
The precipitate was filtered out, washed several times with water and dried to obtain 70 parts of solid aluminum 2-hydroxy-1-~9~

1 naphthoate.
Into a mixture of 2 parts of castor oil 20 parts of toluene 20 parts of ethyl acetate and 20 parts of n-hexane was dissolved 8 parts of nitro cellulose to obtain a homogeneous solution. Into the solution was mixed 20 parts of the above-described aluminum 2-hydroxy-1-naphthoate and 7 parts of silicon oxide (Trade Mark "Siloide") followed by homogeneously dissolving or dispersing by a ball mill to obtain a developer ink. The resulting ink was diluted with xylol to give a viscosity of about 1 poise and subjected to a gravure printing process to give about 2 g/m2 of dried coating film.
Example 9 80 parts of sodium anacardate prepared according to the aforementioned method was dissolved in 150 parts of hot water and into the solution was added with stirring a solution of 20 parts of zinc sulfate in 150 parts of hot water to obtain zinc anacardate. The mixture was concentrated to a total weight of 200 parts and then mixed with a mixture of 40 parts of ethyl cellulose, 70 parts of ethyl cellulose, 150 parts of ethanol and .20 40 parts of titanium oxide followed by completely dissolving or dispersing by a ball mill to afford a developer ink in the form of an emulsion. The ink was diluted with ethanol to give a viscosity of about 1 poise and subjected to a flexographic printing process to give about 3 g/m2 of dried coating film.
Comparative test 6 The above-described paper coated with microcapsules containing crystal violet lactone was piled on each of the surfaces printed with each color developer ink in the Examples and pressurized under pressure load of 600 kg/m2 to form color ~30 images. After allowed to stand in the dark for an hour, the ~LQ~

1 spectral absorption curve was measured within the wave length ranging from 400 to 700 m~, the density at the absorption maximum was defined as fresh density.
After further irradiating sunlight for 1 hour and for 3 hours, the spectral absorption curve of the color images was measured and its light resistance was calculated according to the following equation.

Density at the absorption maximum . . after irradiation of sunliqht Llght reslstance (%) = - x 100 Fresh density at the absorption .10 maximum The results are summarized in the following T.able 6.

Fresh density Light resistance Light resistance (%) (%) after 1 hour after 3 hours irradiation of irradiation of sunlight sunlight ..
Example 5 0.75 82 70 6 0.91 . 87 79 7 0.86 89 85 8 0.89 84 78 ~20 9 0.73 80 71 From the Table 6, it is evident that the developer inks of the present invention are superior in their developing ability and light resistance even in the case of thin printed layer of 3 g/m Comparative test 7 A paper coated with microcapsules containing 3-methyl-2,2'-spirobi (benzo[f~chromene) was placed on each of the surfaces printed with the color developer ink in the above-described ~30 Examples, and its fresh density and light resistance were measured c~

1 in the same manner as described above in Comparative test 6.

, Fresh density Light resistance Light resistance (%) (%) after 1 hour after 3 hours irradiation of irradiation of sunlight sunlight .
Example 5 0.70 70 62 6 0.85 73 65 7 0.73 91 87 8 0.82 79 66 .10 9 0.69 68 58 As apparent from the numerical values in the above-described Table 7, the paper surfaces printed with the developer inks of the present invention show an excellent developing ability also for the color former sheet containing 3-methyl-2,2'-spirobi(benzo[f]chromene). Furthermore, the paper surface printed with the ink containing aluminum silicate hydrate (Osmos N) was remarkably improved in the light resistance of the color developed image o~ 3-methyl-2,2'-spirobi(benzo[f]chromene).
; .20 _30 `

Claims (3)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a recording sheet comprising a support having coated thereon a color developer layer with a color developer capable of forming a distinct color when contacted with a color former, the improvement wherein the color developer is a metallic compound of an aromatic carboxylic acid.

2. The recording sheet as claimed in claim 1 wherein said aromatic carboxylic acid has at least one hydroxyl group in the chemical structure.

3. A pressure sensitive recording paper which comprises in combination: a dyestuff precursor or its solution and a dyestuff acceptor which is capable of color formation by reaction with the dyestuff precursor, wherein said dyestuff acceptor consists es-sentially of the salt a polyvalent metal and of an aromatic carboxylic acid which is selected from the group consisting of 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-iodo-benzoic 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-isopropylbenzo-ic acid, 2, 5-dinitrobenzoic acid, 3, 4-dinitrobenzoic acid, 3, 5-dinitrobenzoic acid, p-tert-butylbenzoic acid, N-phenyl-antra-nillic 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-di-tert-amylsalicylic 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-hydroxy-benzoic acid, p-hydroxybenzoic acid, 3, 5-dinitro-salicylic 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'-methylene-salicylic acid, thiosalicylic acid, trimellitic anhydride, anacardic acid, benzoic anhydride, 2-carboxybenzal-dehyde, and dephenic acid.