US3843383A - Recording sheet employing an aromatic carboxylic acid - Google Patents

Abstract

1. A RECORDING SHEET COMPRISING A SUPPORT HAVING THEREON A LAYER OF COLOR DEVELOPER CAPABLE OF REACTING WITH A SUBSTANTIALLY COLORLESS COLOR TO FORM A COLORED IMAGE WHERIN SAID COLOR DEVELOPER CONSISTS ESSENTIALLY OF AT LEAST ONE CLAY AND AT LEAST ONE AROMATIC CARBOXYLIC ACID OR AN ALKALI METAL SALT THEREOF.

Description

United States Patent 3,843,383 RECORDING SHEET EMPLOYING AN AROMATIC CARBOXYLIC ACID Sadao Ishige, Kanagawa, and Takao Hayashi and Hajime Kato, Shizuoka, Japan, assignors to Fuji Photo Film Co., Ltd., Minami Ashigara-shi, Kanagawa, Japan No Drawing. Filed Oct. 30, 1972, Ser. No. 301,925 Claims priority, application Japan, Oct. 28, 1971, 46/235,834 Int. Cl. B41m 5/00 US. Cl. 11736.8 12 Claims ABSTRACT OF THE DISCLOSURE A recording sheet comprising a support having thereon a layer of color developer capable of reacting with a sub stantially colorless color former to form colored image wherein said color developer comprises at least one clay and at least one aromatic carboxylic acid or an alkali metal salt thereof.

BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a recording sheet and, more particularly, it relates to the improvement in the color developer which reacts with a nearly colorless color former to form a developed color image.

Description of the Prior Art In a recording sheet, as is well known from US. Pats. 2,712,507; 2,730,456; 2,730,457; 3,418,250, etc., microcapsules containing a solution of a nearly colorless organic compound (hereinafter referred to as color former), and a compound which reacts with said color former to develop color (hereinafter referred to as color developer) are utilized.

A variety of forms of application are known. For example, there is a pressure sensitive copying sheet comprising a sheet coated with microcapsules containing color former solution (i.e., color former sheet or upper sheet), a sheet coated with a color developer together with a binder (i.e., color developer sheet or lower sheet) and, in some cases, a sheet one side of which is coated with a color developer and the other side of which is coated with microcapsules (i.e., middle sheet). As another embodiment, there is a sheet wherein the microcapsules and the color developer are applied to the same surface of a support (i.e., single recording sheet).

Furthermore, a heat-sensitive recording sheet is also known which has the same basic elements as above and is coated with a color former and a color developer on the same or different supports. In this case, a heat-meltable material such as acetanilide is added to a layer containing the color former.

As still a further embodiment, a printing process wherein a color developer sheet and a color former ink are combined is also known.

As the above-described color developer, there have generally been used clays such as acid clay, active clay, attapnlgite, zeolite, hentonite, etc., organic acids such as succinic acid, tannic acid, gallic acid, etc., phenol resins, and the like. Acid clay, of course, is commonly available, through produced in Japan, and has properties similar to attapulgite.

However, the use of such materials is subject to the defect that when such color developers are used singly, or even, for example, when clays and a phenol compound are used in combination, the developed color images obtained by the reaction with a color former such as Crystal Violet lactone, 3-methyl-2,2'-spirobi(benzo-f-chromene),

3,843,383 Patented Oct. 22, 1974 ice SUMMARY OF THE INVENTION One object of the invention is to provide an improved recording sheet without losing the advantages of the color developer clays.

Another object of the invention is to improve the light resistance of a developed color image formed by a color former and clays.

The above-mentioned objects of the invention are attained by incorporating at least one aromatic carboxylic acid or an alkali metal salt thereof in a clay used as a color developer.

The term recording sheet as used herein defines a support having thereon at least one color developer layer as described above used for recording utilizing the coloring reaction between a color former and a color developer. Therefore, all the above-stated embodiments are included therein.

DETAILED DESCRIPTION OF THE INVENTION As the clays used in the invention, there can be illustrated, for example, acidic clay, active clay, attapulgite, zeolite, bentonite, kaolin, silicic acid, synthetic silicic acid, aluminum silicate, zinc silicate, etc. Colloidal silicic acid and the like may also be employed as the clays in accordance with the invention. In general, any of the may clay materials used by the prior art to react with a colorless basis dye to yield a colored reaction product may be used in the present invention. Clays prepared by chemically processing such clays can also be employed; for instance, those clays which have been subjected to known treatments with a mineral acid or alkaline material to improve certain properties thereof. Such clays may also be subjected to physical processing, e.g., crushing, to reduce the particle size thereof, if desired.

As the aromatic carboxylic acid used in the present invention there are aromatic compounds having at least one carboxyl group, e.g., benzoic acid, aminobenzoic acid (the 0-, mand p-derivatives can be used), hydroxybenzoic acid the o-, mand p-derivatives can be used), nitrobenzoic acid (the o-, mand p-derivatives can be used), 2-hydroxy-3-naphthoic acid, 2-hydroxyl-1-naphthoic acid, 4-amino-1-naphthoic acid, 4-nitro-2-hydroxyl-l-naphthoic acid, 2,4-dihydroxy-benzoic acid, 2,4,6-trihydroxy-benzoic acid, 2-hydroxy-4-aminobenzoic acid, acetaminobenzoic acid (the o-, mand pderivatives can be used), 2-hydroxyA-methylbenzoic acid, 2-amino-4-tert-butylbenzoic acid, 2,6-dihydroxy-4-ethylbenzoic acid, 2-hydroxy 5-tertbutylbenzoic acid, 3-phenylsalicylic acid, 3-methyl-5-tertbutylsalicylic acid, 3,S-di-tert-butylsalicylic acid, 3,5-ditert-amylsalicyclic acid, 3-cyclohexylsalicylic acid, 5-cyclohexylsalicylic acid, 3-methyl-5-isoamylsalicylic acid, 3, S-di-sec-butylsalicylic acid, 5 sec-butylsalicylic acid, 5- nonylsalicylic acid, 3,S-di-isopropylsalicylic acid, and the like. Of these compounds, those having at least one hydroxy group are particularly effective.

As the alkali metal salts of the organic carboxylic acid, there can be illustrated, for example, sodium, lithium, or potassium salts of the above-mentioned organic carboxylic acids, and the like.

In the case of these mental salts, aromatic'carboxylic acids having at least one or more hydroxyl groups are especially effective.

The most preferred organic carboxylic acids or alkali metal salts thereof used in the present invention have at least one hydroxyl group and further one or more alkyl groups with 4 to 12 carbon atoms, a phenyl group and/ or a cyclohexyl group.

The amount of the aromatic carboxylic acid or alkali metal salt thereof is preferably about 1 to about 200 parts by weight, more preferably to 60 parts by weight, based on 100 parts by weight of the clay. While lesser amounts can be used, insufficient results are often encountered, and at much greater amounts the improvement in results is not significantly bettered in most cases to warrant the use of additional acid.

As the process for producing the color developer in accordance with the invention, there are, for example, the following processes, but the present invention is not limited to the following production examples, since the etfects of the invention naturally occur when at least one or more clays and at least one or more aromatic carboxylic acids or alkali metal salts thereof co-exist.

(1) At least one aromatic carboxylic acid or an alkali metal salt thereof is dissolved or dispersed in water and then a clay is dispersed therein with stirring. Thereafter, the pH of the dispersion is adjusted to a value suitable for the clay used, and a binder such as a latex, polyvinyl alcohol, gum arabic, starch, etc. is added thereto to prepare a coating solution. The amount of the binder is usually greater than about 5 parts by weight and is preferably to parts by weight per 100 parts by weight of the clay.

The resultant coating solution is applied to a support such as a paper, paper substitute, film, etc. in an amount of above about 3 g./m. preferably 4 to 8 g./m. then dried. In this production process, an amount of aromatic carboxylic acid or the salt thereof greater than about 0.5 parts by weight, preferably 5 to about 200 parts by weight, per 100 parts by weight of the clay is preferred.

(2) After dispersing the clay in water, the pH of the dispersion is adjusted to a value appropriate for the clay used. Then, a binder is added thereto. The amount of the binder used is above about 5 parts by weight, preferably 10 to about 30 parts by weight, per 100 parts by weight of the clay.

The coating solution prepared as above is then applied to a paper, resin film or paper substitute in an amount of above about 3 g./m. preferably 4 to 8 g./m.

Thereafter, an aromatic carboxylic acid or an alkali metal salt of an aromatic carboxylic acid is dissolved or dispersed in water or an organic solvent such as methanol, ethanol, benzene, acetone, ethyl acetate, etc., and, if necessary, in the aqueous system, a binder such as a latex, polyvinyl alcohol, maleic anhydride-styrene copolymer, etc., preferably which dissolves in the aqueous system, is added, or, in the organic solvent system, a binder such as ethyl cellulose, styrene-butadiene copolymer, etc. is added thereto.

The resulting coating solution is then applied to the previously coated clay to obtain a co-existing system of clay and an aromatic carboxylic acid or the alkali metal salt thereof. In this case, the amount of the binder used is suitably less than about 10 parts by weight per 100 parts by weight of the aromatic carboxylic acid or alkali metal salt thereof and the amount of the coating solution is suitably above about 0.1 g./m. desirably 0.3 to 1.0 g./m. The upper limit of the amount coated is decided primarily by economic considerations.

The dispersion pH adjustment referred to above is accomplished by adding an alkaline material to the dispersion to render the pH thereof alkaline. This preferred step increases the color developing ability of the system, with best results usually being provided at a pH of from about 8 to about 10.5. Any alkaline material compatible with recording sheet systems can be used, but normally an 4 alkali hydroxide is used because of the high solubility of such compounds.

In the above-described case where an organic solvent is used, the effect of the invention becomes larger when a solvent capable of dissolving the aromatic carboxylic acid or the alkali metal salt is used. :In such cases, binders are rarely required, though if used they preferably are dissolved in the organic solvent.

There is no limit on the binder which may be used in the present invention, that is, the binder used in the present invention can be selected from any of those as are used in the prior art, and the exact binder used is not overly critical. Examples of binders in addition to those listed above which can be used are gelatin, casein, sodium alginate, carboxymethylcellulose, a latex of a material such as polyvinylacetate, styrene-butadiene copolymers, styrene-acrylic acid copolymers, butadiene-acrylic acid copolymers or polyacrylates.

The layer containing the color developer of the invention may further contain acidic resins such as a phenolformaldehyde resin, or inorganic pigments such as metal oxides, metal hydroxides, etc.

Preferred phenol resins are described in U.S. Pats. 3,516,845; 3,427,180; and 3,455,721, for example, a pphenylphenol-formaldehyde condensate, a p-tert-butylphenol-formaldehyde condensate or a phenol-acetylene condensate.

Preferred inorganic pigments include metal oxides such as Zinc oxide, magnesium oxide or titanium oxide, metal hydroxides such as calcium hydroxide, magnesium hydroxide or zinc hydroxide, and metal carbonates such as magnesium carbonate, zinc carbonate and calcium carbonate.

In addition, each coating solution may be applied to either the whole surface or may be only partly coated (printed) on the surface.

The coating solution prepared in the above examples may be coated on a support together with the color formers described hereinafter. When used as a pressure sensitive paper, the color former may be contained in microcapsules.

The color former is usually dissolved in a solvent well known in the art, such as chlorinated diphenyl, chlorinated parafiin, benzene, toluene, etc., and encapsulated in microcapsules, or is dissolved in the above-described solvent and, after adding a binder thereto, applied to a support. In the latter case, the solution may be supplied to a color developer sheet through a stencil or like pattern in ink-like form instead of coating onto the support. In the case of a heat-sensitive copying paper, known heat-meltable materials such as acetanilide, urea, alphaor beta-naphthol, phthalic anhydride, stearic acid, etc. are mixed with the color former and applied to a support. Preferably the ratio of thermofusible substance to the color former is 1.5 to 30 wt. percent.

As described above, with respect to the color former, the solvent therefor, the additives thereto, encapsulating methods, etc., any of those known in the art can be suitably selected and employed.

However, the kind of color former used is not critical in this invention. Examples of the color former usable in this invention are triarylmethane compounds such as 3,3 bis(p dimethylaminophenyl) 6 dimethylamino phthalide, i.e., Crystal Violet Lactone 3,3-bis(p dimethyl-aminophenyl) phthalide, i.e., malachite green lactone, 3 (p dimethylaminophenyl) 3 (1,2-dimethylllldOl 3 yl)phthalide, 3 (p dimethylaminophenyl)- 3-(2 methylindol 3 yl)phthalide, 3-(p-dimethylaminophenyl) 3 (2-phenylindol-3-yl)phthalide, 3,3-bis( 1,2,- dimethylindol 3 yl)-5-dimethylaminophthalide, 3,3- bis( 1,2-dimethylindol 3 yl)-6-dimethylatninophthalide, 3,3 bis(9-ethylcarbazol-3-yl) 5 dimethylaminophthallcle, 3,3-bis(2 phenylindol 3 yl)-5-din1ethylaminophthalide, and 3 p dimethylaminophenyl-3-(l-methylpyrrol 2 yl) 6 dimethylamino-phthalide; diphenyl methane compounds such as 4,4'-bis-dimethyl aminobenzhydrine benzyl ether, N-halophenyl-leuco Auramine and N-2,4,5-trichl0rophenyl leuco Auramine; xanthene compounds such as rhodamine-B anilinolactam, rhodamine (p-nitroanilino)lactam, rhodamine B (p-chloroanilino)lactam, 7 dimethylamino 2 methoxyfluoran, 7-diethylamino 2 methoxyfluoran, 7 diethylamino-3- methyoxyfluoran, 7 diethylamino 3 chlorofluoran, 7-diethylamino 3 chloro 2 methylfluoran, 7-diethylamino-2,3 dimethylfluoran, 7-diethylamino (3-acetylmethylamino)fiuoran, 7-diethylamino (3 methylamino)fluoran, 3,7 diethylaminofluoran, 7 diethylamino-3- (dibenzyl-amino)fluoran, 7 diethylamino 3 (methylbenzylamino)fiuoran, 7-diethylamino 3 (chloroethylmethylamino)fluoran and 7-diethylamino 3 (diethylamino)fluoran; thiazine compounds such as benozyl leucomethylene blue and p-nitrobenzyl leucomethylene blue; and spiropyran compounds such as 3-methyl-spiro dinaphthopyran 3 ethyl-spiro-dinaphthopyran, 3,3-dichloro-spiro-dinaphthopyran, 3-benzyl-spiro dinaphthopyran, 3-methyl naphtho (3-methoxybenzo)spiropyran and 3-propyl-spiro-dibenzopyran.

In general, a combination of crystal violet lactone which has a rapid color-forming property when contacted with clay, and benzoyl leucomethylene blue which has a slow color-forming property but which is capable of forming a color of greater light-resistance is preferably used.

However, when a sheet having thereon microcapsules containing the color former of the above described combination is contacted, for example, under pressure, with a conventional clay-coated paper or a color developer sheet wherein a phenol resin is used, a long time is required before benzoyl leucomethlene blue forms a color after the momentary color formation of the Crystal Violet lactone, and, in addition, the developed color image of Crystal Violet lactone becomes faint.

In a color developing sheet utilizing a phenol resin, this tendency is particularly great, because benzoyl leucomethylene blue scarcely forms any color.

When the color developer in accordance with the invention is used, the above-described defect is completely removed.

In short, the recording sheet of the invention is characterized by a color developer wherein clays and at least one aromatic carboxylic acid or an alkali metal salt thereof is used, and, as a result, various capabilities required for a color developer, such as light resistance of the developed color image and the like are remarkably improved.

(1) Light resistance of the developed color image The developed color image formed by using the color developer of this invention does not fade as much when it is irradiated with sun-light or left in a room, as compared to a conventional clay-coated paper. This markedly contributes to the market value of the product.

(2) Color-developin g ability The color-developing ability of the color developer in accordance with the present invention is so improved, as compared with a conventional clay-coated paper, that either the amount of the color developer on a support or the amount of the color former on a color former sheet can be reduced to obtain the same color density.

In particular, the reduction in the amount of the color former used results in reducing the cost of producing recording sheets.

(3) Activity with the passage of time The activity of a conventional clay-coated paper is reduced with the passage of time due to the adsorption of ambient materials, whereas with the color developer of this invention a reduction in the color-developing ability with the passage of time is hardly observed.

It will now be shown by the following Examples of the color developer of the invention, i.e., the color developer wherein at least one aromatic carboxylic acid and/ or an alkali metal salt thereof is incorporated in a clay, has a markedly improved market value as compared with a conventional color developer clay. The present invention, of course, is not to be limited only to such Examples, however.

The effect of the recording sheet of the invention was confirmed using the following color former.

The microcapsules containing the color former were prepared according to the description of, for example, US. Pat. 2,800,457 Green et al. A specific example thereof is shown below. Hereafter, parts are all by weight unless otherwise indicated.

10 Parts of acid-processed pigskin gelatin and 10 parts of gum arabic were dissolved in 400 parts of 40 C. water, and 0.2 parts of Turkey red oil was added thereto as an emulsifying agent. 40 parts of color former-containing oil was emulsified in the resulting solution, the color former-containing oil being prepared by dissolving 2% of Crystal Violet lactone in a mixed oil comprising 4 parts of chlorinated diphenyl and 1 part of lamp oil.

When the size of the oil droplets became 5 microns on the average, emulsification was discontinued, 40 C. water was added thereto to make the total 900 parts, and stirring was continued. Thereafter, the pH of the solution was adjusted to 4.0 to 4.2 by the addition of 10% aqueous acetic acid to cause coacervation.

After stirring for a further 20 minutes, the solution was cooled with ice Water to cause gelation of the coacervate membrane deposited around the oil droplets.

When the temperature of the solution became 20 C., 7 parts of 37% formalin was added thereto. At 10 C., the pH of the solution was adjusted to 9 by the addition of a 15% aqueous sodium hydroxide solution. The addition of sodium hydroxide was conducted slowly. Subsequently, the temperature of the solution was raised to 50 C. over a 20 minute period while stirring.

After adjusting the temperature of the microcapsule dispersion thus obtained to 30 C., the dispersion was applied to a 40 g./cm. paper in coated amount of 6 g./m. (solid components) and then dried.

In the manner as described above, there was obtained a sheet having thereon microcapsules containing as the color former Crystal Violet lactone.

Microcapsule-coated sheets containing other color formers were also prepared in the same manner as above merely by changing the identity of the color former.

The following developer materials were then formed. The particle size of the clay materials used in the examples was 5 microns.

EXAMPLE 1 8 Parts of a 20% aqueous sodium hydroxide solution was added to 300 parts of water, and 10 parts of the following aromatic carboxylic acid was dissolved or dispersed therein. Thereafter, parts of acid clay was gradually added thereto with stirring. 20 g. (solid components) of styrene-butadiene latex (SBR latex) was added thereto, and the pH of the dispersion was adjusted to 9.5 by the addition of a 20% aqueous sodium hydroxide solution.

The coating solution so obtained was applied onto a 40 g./m. base paper to provide a 5 g./m. solid component coating thereon by means of a coating rod, then dried. There was thus obtained a color developer sheet in accordance with the invention.

EXAMPLE 2 100 Parts of acid clay was dispersed in 300 parts of water with stirring. Subsequently, 15 parts of the following aroma-tic carboxylic acid or the alkali metal salt thereof was added thereto. Then, a 20% aqueous sodium hydroxide solution was gradually added thereto and, at a pH of 8, 20 parts (solid components) of SBR latex was added thereto and the pH of the solution was adjusted to 9.5 with the aqueous sodium hydroxide solution. The coating solution thus obtained was applied to a 40 g./n1. base paper to provide a g./m. solid component coating thereon by means of a coating rod, then dried. There was thus obtained a color developer sheet in accordance with the invention EXAMPLE 3 After dispersing 100 parts of finely pulverized silicic acid in 300 parts of water, parts of the following aromatic carboxylic acid or the alkali metal salt thereof was added thereto, and subsequently, 100 parts of a aqueous polyvinyl alcohol solution was added thereto. Thereafter, the pH of the dispersion was adjusted to 6.0 with a 20% aqueous sodium hydroxide solution. The coating solution thus obtained was applied to a 40 g./m. base paper to provide 4 g./m. solid components coating by means of a coating rod, then dried. There was thus obtained a color developer sheet in accordance with the present invention.

EXAMPLE 4 100 parts of acid clay was dispersed in 300 g. of water with stirring. Subsequently, 5 parts of the following aromatic carboxylic acid and 5 parts of the following alkali metal salt of the aromatic carboxylic acid were added thereto. Then, a 10% aqueous sodium hydroxide solution was gradually added thereto and, at a pH of 8, 20 parts (solid components) of SBR latex was added thereto. Further, the pH of the solution was adjusted to 9.5 with a 10% aqueous sodium hydroxide solution. The coating solution thus obtained was applied to a 40 g./m. base paper to give a 5 g./m. solid component coating by means of a coating rod. There was obtained a color developer sheet in accordance with the present invention.

EXAMPLE 5 8 Parts of a 20% aqueous sodium hydroxide solution was added to 300 parts of water, and 100 parts of acid clay was gradually dispersed therein with stirring. Thereafter, 20 parts (solid component) of a SBR latex was added thereto to prepare a coating solution. The pH of the coating solution was 9.5.

The resulting coating solution was applied to a 40 g./m. base paper to give a 5 g./m. solid component coating thereon by means of a coating rod, then dried.

Thereafter, 50 parts of the following aromatic carboxwas thus obtained a color developer sheet in accordance with the invention.

Comparative Example 1 100 Parts of acid clay was dispersed in 300 parts of water with stirring, and 8 parts of a 20% aqueous sodium hydroxide solution was added and then 20 parts (solid component) of SBR latex was added thereto to prepare a coating solution. The pH of the resulting coating solution was 9.5.

This coating solution was applied to a 40 g./ m base paper so that 6 g./m. of solid components were coated thereon by means of a coating rod.

Comparative Example 2 100 Parts of finely pulverized silicic acid was dissolved in 30 parts of water, 100 parts of a 20% aqueous polyvinyl alcohol solution was added thereto, and the pH of the dispersion was adjusted to 6.0 with a 20% aqueous sodium hydroxide solution. The resulting coating solution was then applied to a 40 g./m. base paper so that 4 g./m. of solid components were coated thereon by means of a coating rod, then dried.

Comparative Test and the Results Obtained A microcapsule-coated sheet containing Crystal Violet lactone or 2,4-dimethyl-7-diethylaminofiuoran prepared as heretofore described was superposed on each of the color developer sheets prepared in Examples 1-5 and Comparative Examples 1 and 2, and color was developed by applying a load of 600 kg/cm. thereto.

After leaving the developed sheets for one day and one night in the dark, the reflection absorption spectrum between 380-700 111 1. in wavelength was measured by means of a DB-type Beckman spectrophotometer, and the absorbance (hereinafter referred to as density) at the absorption maximum was regarded as the fresh or initial density. Furthermore, the color-developed bodies were exposed to sun-light for one hour, and the reflection absorption spectrum at the color-developed surface was measured to determine the density.

From the data thus obtained, the light resistance value defined by the following formula was determined:

Light resistance value (percent) ylic acid or the alkali metal salt thereof was dissolved The density f the color developed body after or dispersed 1n 300 parts of ethanol 1n which 5 parts of ex Osure to sum ht th 1 cellulose had previously been dissolved The resultp g X100 y Fresh density of the color-developed body mg coating solution was applied to the above-described acidic lay coated paper in an amount of 0.5 g./m. (solid The fresh density and the light res1stance values thus component) by means of a coating rod, then drled. There determined are given 1n Table 1.

TABLE 1 2,4-dimethyl-7- Crystal violet lactone diethylaminofiuoran Example or Light Light comparative Aromatic carboxylic acid or the Fresh resistance, Fresh resistance, example alkali metal salt thereof density percent density percent Number:

1 Example 1 1. 01 77. 2 0. 83 99. 3 Comparative 0. 00 59. 8 0. 79 84. 7

Example 1. Example 1 3,5-di-tert-butylsalicylic acid 1.02 76. 4 0.80 96. 2 do m-Nitrobenzoic acid 0.99 63.5 0.82 87.3 P-Aminobcuzoic acid. 0. 98 71.5 0.78 89.5 P-Anisic acid 0. 99 60. 2 0. 79 88. 8 2,4-di-hydroxybenzoic acid--. 1.03 78. 3 0. 84 91. 2 2-naphthoic acid 1. 00 72. 3 0. 79 96. 0 1.02 76.5 0.81 97.1 y 1. 04 77. 5 O. 82 98. 6 S-tert-butylsalicylic acid sodium salt 1.02 74. 3 0.80 97. 8 Potassium 2-hydroxy-3-naphthoate. 1. 00 72. 6 0. 81 92. 3 m-Hydroxybenzoic acid 1.01 73.6 0.79 91.5 Salicylic acid 1. 03 74.3 0.82 90. 5 Comparative 1. 00 48. 9 0. 81 72. 1

Example 2. 14 Example 4 Salicylic acid and sodium 5-tert-butyl- 1.02 73.1 0.80 91.2

salicylate. 3,5-di-tert-butylsalicylic acid and potassium 1.05 74. 2 0.82 93. 6

rn-hydroxybenzoate. Sodium 5-sce-butylsalicylate 1.01 48. 4 0. 83 85. 9 Salicylic acid 1.02 76. 9 0.82 98. 2 1. 00 75. 0 0. 81 97. 9

From the results of the data in Table 1, it is seen that the light resistance of a color-developed body can markedly be improved by the use of a clay and at least one arom-atic carboxylic acid or an alkali metal salt thereof.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be aparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

What is claimed is:

1. A recording sheet comprising a support having thereon a layer of color developer capable of reacting with a substantially colorless color to form a colored image wherein said color developer consists essentially of at least one clay and at least one aromatic carboxylic acid or an alkali metal salt thereof.

2. The recording sheet of claim 1 wherein the color developer is an acidic clay.

3. The recording sheet of claim 1 wherein the color former is a basic dye.

4. The recording sheet of claim 1 wherein from about 1 to about 200 parts by weight of said aromatic carboxylic acid or alkali metal salt thereof is present per 100 parts by weight of said clay.

5. The recording sheet of claim 1 wherein the arcmatic carobxylic acid or alkali metal salt thereof is substituted with at least one hydroxyl group.

6. The recording sheet of claim 5 wherein the aromatic oarboxylic acid or alkali metal salt thereof is also substituted with one or more alkyl groups having 4 to 12 carbon atoms, a phenyl group or a cyclohexyl group.

7. The recording sheet of claim 1 wherein the constituents are carried in a binder.

8. The recording sheet of claim 7 wherein about 5 to 30 parts by weight of binder are present based on 100 parts by weight of clay.

9. The recording sheet of claim 1 wherein from 5 to parts by weight of said aromatic carboxylic acid or alkali metal salt thereof is present per parts by weight of said clay.

10. The recording sheet of claim 1 being pressuresensitive copy sheet.

11. The recording sheet of claim 7 wherein up to about 30 parts by weight of binder are present based on 100 parts by Weight of clay.

12. In a process for developing a color image on a recording sheet by the reaction between a clay and a colorless color former, the improvement which comprises carrying out said reaction in the presence of an aromatic carboxylic acid or alkali metal salt thereof.

References Cited UNITED STATES PATENTS 3,746,563 7/1973 Farber et al 11736.2 3,664,858 5/1972 Huffman 11736.8 3,689,302 9/1972 Kubo et al 11736.8 3,418,250 12/1968 Vassiliades 11736.2 X 3,427,180 2/1969 Phillips 1l7-36.8 X

THOMAS J. HER'BERT, JR., Primary Examiner US. Cl. X.R. 252316

Claims (1)

1. A RECORDING SHEET COMPRISING A SUPPORT HAVING THEREON A LAYER OF COLOR DEVELOPER CAPABLE OF REACTING WITH A SUBSTANTIALLY COLORLESS COLOR TO FORM A COLORED IMAGE WHERIN SAID COLOR DEVELOPER CONSISTS ESSENTIALLY OF AT LEAST ONE CLAY AND AT LEAST ONE AROMATIC CARBOXYLIC ACID OR AN ALKALI METAL SALT THEREOF.