Recording sheet

Abstract

A recording sheet comprising a support having thereon a color developer layer capable of reacting with a color former to form color images, said color developer layer containing (1) a metal compound of an aromatic carboxylic acid and (2) at least one member selected from the group consisting of ethers and alcohols.

Description

BACKGROUND OF THE INVENTION

1. FIELD OF THE INVENTION

The present invention relates to a recording sheet, and more particularly to a recording sheet containing an improved color developer.

2. DESCRIPTION OF THE PRIOR ART

Recording sheets utilizing a color reaction of an almost colorless organic compound (hereinafter referred to as a "color former") such as Malachite green lactone, benzoylleucomethylene blue, crystal violet acetone, Rhodamine B lactam, 3-dialkylamino-7-dialkylaminofluoran and 3-methyl-2,2'-spirobi (benzo[f]chromene), and an adsorbent or reactive material (hereinafter referred to as a "color developer") capable of forming a color when contacted with the color former are well known.

As the recording sheets practically using the phenomenon, there are a pressure-sensitive recording sheet (see, for example, U.S. Pat. Nos. 2,505,470; 2,505,489; 2,550,471; 2,548,366; 2,730,456; 2,730,457; 3,418,250, etc.) and a heat-sensitive recording sheet (see, for example, Japanese Patent Publication Number 4160/68; U.S. Pat. No. 2,939,009, etc.). Further, a printing method is known wherein an ink containing the color former is applied to the color developer sheet through a medium such as a stencil (see German Patent OLS No. 1,939,62, etc.).

In many cases, the above mentioned phenomenon of the color reaction between the color former and the color developer requires physical conditions such as pressure with a pen or with a key of a typewriter, heat, etc.

As the most representative embodiment of the recording sheets, there is illustrated a pressure-sensitive copying paper. A pressure-sensitive copying paper may be obtained by dissolving a color former in a solvent such as chlorinated paraffin, alkylnaphthalene, alkylated diphenylethane, alkylated diphenylmethane, or the like, dispersing the resulting solution in a binder or microencapsulating the solution, and then the coating on a support such as paper, plastic film, etc.

A heat-sensitive recording sheet may be obtained by coating a color former on a support together with a thermofusible material such as acetanilide. As used herein, the term "thermofusible material" means a material which is melted on heating to dissolve the color former.

In general, the color former and color developer may be coated on the same surface or opposite surfaces of a support, or on different supports. Also, the color developer may be coated on or impregnated into a support as an ink.

As the above-described color developer, clays such as acid clay, activated clay, attapulgite, zeolite, bentonite, etc.; organic acids such as succinic acid, tannic acid, gallic acid or phenol compounds, and acidic polymers such as phenol resins are known. Furthermore, a mixture of an aromatic carboxylic acid and a metal compound; a metal compound of a polymer of an aromatic carboxylic acid having at least one hydroxy group and an aldehyde; a metal compound of an aromatic carboxylic acid; a metal compound of a phenol compound having a pKa of not more than 8; and the like, are effective as a color developer.

Of these, a metal compound of an aromatic carboxylic acid is particularly effective as a color developer. That is, a color developer sheet containing as a color developer a metal compound of an aromatic carboxylic acid has the following excellent properties in comparison with conventional color developer sheets.

1. Even when left in the air, reduction in color-developing ability with the passage of time is small.

2. By using an aromatic carboxylic acid difficult to dissolve in water, disappearance or reduction in density can be avoided even when the color former on the color developer sheet is wet with water.

3. The light fastness of the colored image on the color developer sheet is excellent.

4. Since sufficient color-developing ability can be obtained using a small coating amount, workability in coating is very good.

As is described above the properties of the recording sheet and the various problems encountered in the production thereof have been improved considerably by using a metal compound of an aromatic carboxylic acid as a color developer instead of the conventional color developers.

However, there remain the disadvantages that, in the production of a metal compound of an aromatic carboxylic acid, the viscosity of the prepared (coating) solution increases and the particle size of the metal compound becomes coarse thereupon. Therefore, it is difficult to prepare a stable coating solution and, unless the particle size of the metal compound is made fine by means of a ball mill or sand mill, there is room for improvement in the color-developing ability and film surface strength of the coated layer.

A primary object of the present invention is to improve the color-developing ability of a color developer sheet containing a metal compound of an aromatic carboxylic acid.

Another object of the present invention is to simplify the steps for preparing a coating solution containing an aromatic carboxylic acid.

Further object of the present invention is to improve the coating characteristics of the coating solution containing an aromatic carboxylic acid.

Still a further object of the present invention is to provide a color developer having the above-described advantages.

Still a further object of the present invention is to provide a recording sheet having the above-described advantages.

SUMMARY OF THE INVENTION

As a result of various investigations, it has been found that the addition of at least one member selected from the ethers and alcohols to a color-developing layer containing a metal compound of an aromatic carboxylic acid achieves the above-described objects.

DETAILED DESCRIPTION OF THE INVENTION

The ethers suitable for use in this invention can be represented by the formula,

ROX

wherein X is --(CH.sub.2).sub.p OR', --(CH.sub.2).sub.p OH, --[(CH.sub.2).sub.n O].sub.q H, --[(CH.sub.2).sub.n O].sub.q R", an alkyl group (preferably, having up to 18 carbon atoms) or an alkenyl group (preferably, having up to 18 carbon atoms), R is an alkyl group (preferably, having up to 10 carbon atoms), an aryl group (preferably, having up to 10 carbon atoms) or an alkenyl group (preferably, having up to 10 carbon atoms), R' and R" each is an alkyl group (preferably, having up to 18 carbon atoms), an aryl group (preferably, having up to 18 carbon atoms) or an alkenyl group (preferably, having up to 18 carbon atoms), p is an integer of 1 to 20 (preferably, 2 or 3), and q is an integer of 2 to 30.

As specific examples of the ethers, ethers such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, diethylene glycol mono-n-butyl ether, ethylene glycol monophenyl ether, diethylene glycol dimethyl ether, 3-methoxybutyl acetate, ethylene glycol monoethyl ether, ethylene glycol diethyl ether, diethylene glycol acetate monoethyl ether, ethylene glycol diphenyl ether, ethylene glycol dimethyl ether, ethylene glycol monobutyl ether, ethylene glycol monopropyl ether, ethylene glycol monobenzyl ether, ethylene glycol monooctyl ether, ethylene glycol monododecyl ether, diethylene glycol monoethyl ether, dipropylene glycol monomethyl ether, polyoxyethylene cetyl alcohol ether, polyoxyethylene oleyl alcohol ether, polyoxyethylene stearyl alcohol ether, polyoxyethylene lauryl alcohol ether, polyoxethylene octyl alcohol ether, polyoxyethylene butyl alcohol ether, polyoxyethylene nonyphenol ether, etc are suitable.

The alcohols are preferably aliphatic alcohols having 1 to 18 carbon atoms, although other alcohols can be employed. Specific examples are alcohols such as n-butyl alcohol, n-amyl alcohol, n-hexyl alcohol, n-heptyl alcohol, n-octyl alcohol, n-nonyl alcohol, n-decyl alcohol, lauryl alcohol, myristyl alcohol, cetyl alcohol, stearyl alcohol, isobutyl alcohol, sec-butyl alcohol, isoamyl alcohol, tert-butyl alcohol, sec-butyl carbinol, diethyl carbinol, 1-hexanol, 2-hexanol, 3-hexanol, cyclohexanol, 3-methyl-1-pentanol, 4-methyl-2-hexanol, allyl alcohol, trans-crotyl alcohol, ciscrotyl alcohol, 2-methyl-3-buten-1-ol, o-tolyl carbinol, m-tolyl carbinol, p-tolyl carbinol, benzyl alcohol, etc., are suitable. Mixtures of ethers and alcohols can be used where desired.

Of the ethers to be used in the invention, glycol ethers are particularly desirable and, of the alcohols, alcohols having 4 or more carbon atoms are particularly preferable. That is, when a glycol ether or an alcohol having 4 or more carbon atoms is used, the color-developing ability is markedly improved and, when they are used in combination, the color-developing ability is improved to an even greater extent. In addition, when an alcohol having 4 or more carbon atoms is used, water-immersion coloration of the color developer layer is depressed. As used herein, the term "water-immersion coloration" means the phenomenon of the coloring of the color former upon immersing in water the color developer layer in face-to-face contact with a color former layer followed by drying.

A suitable amount of the ethers and alcohols which can be used is from 10 to 250 parts by weight, preferably 50 to 150 parts by weight, per 100 parts by weight of the aromatic carboxylic acid.

The metal compound of the aromatic carboxylic acid to be used in the color developer sheet of the invention is the compound prepared by reacting an alkali metal salt, such as the sodium or potassium salt, of an aromatic carboxylic acid with a water-soluble metal salt in a solvent in which both are soluble. Generally, the alkali metal salt of the aromatic carboxylic acid and the water-soluble metal salt may be reacted with each other in optional porportions, but preferably, they are reacted in gram equivalent amounts.

The metal compound of an aromatic carboxylic acid is a salt of such an acid such as a zinc, tin, aluminum, nickel, magnesium or calcium salt of an aromatic carboxylic acid, and these salts can be obtained easily by stirring an aromatic carboxylic acid or an alkali metal salt thereof with a metal hdyroxide, sulfate or nitrate in the presence of an alkali. In this procedure, the pH value, temperature and pressure are not critical.

The aromatic carboxylic acid is preferably represented by the formula: ##SPC1##

wherein R may be the same or different and represents a hydrogen atom, a hydroxy group, a halogen atom such as chlorine, a nitro group, an alkyl group having 1 to 10 carbon atoms (preferably 3 to 6 carbon atoms), of which the total carbon atoms are less than 13, an aryl group such as phenyl group, an arylamino group such as anilino group, and an alicyclic group such as hexyl group, m is an integer of 0 to 7 and n is an integer of 0 to 5, and the aromatic carboxylic acid may be dimerized through the substituent R as a methylene group.

More preferable compounds are those represented by the formula, ##SPC2##

wherein R, m and n are as defined above.

The most preferable compounds are those represented by the formula ##SPC3##

wherein R is as defined above, n is 1 or 2, and R is attached to the meta-position relative to the hydroxy group.

Above all, aromatic carboxylic acids having at least one hydroxyl group are especially effective and those having a hydroxyl group in the o-position, i.e., the aromatic carboxylic acids represented by the following formulae, are more effective. ##SPC4##

wherein R, m and n are as defined above.

The aromatic carboxylic acid used in the present invention includes, for example, benzoic acid, nitrobenzoic acid (any of o-, m- and p-derivatives may be used), chlorobenzoic acid (any of o-, m- and p-derivatives may be used), toluic acid (any of o-, m- and p-derivatives may be used), 4-methyl-3-nitrobenzoic acid, 2-chloro-4-nitrobenzoic acid, 2,3-dichlorobenzoic acid, 4-methyl-3-nitrobenzoic acid, 4-acetylbenzoic acid, 2,4-dihydroxybenzoic acid, 2,5-dihydroxybenzoic acid, 1-naphthoic acid, 2-naphthoic acid, 1-hydroxy-2-naphthoic acid, 2-hydroxy-3-naphthoic acid, 2-hydroxy-1-naphthoic acid, thiosalicyclic acid, salicylic acid, 3,5-dinitrosalicyclic acid, 3-methylsalicyclic acid, 2,4-cresotinic acid, 2,5-cresotinic acid, 3-methylsalicylic acid, 2,4-cresotinic acid, 2,5-cresotinic acid, 5-tert-butylsalicylic acid, 3-phenylsalicylic acid, 3-methyl-5-tert-butylsalicylic acid, 3,5-di-tert-butylsalicylic acid, 3,5-di-tert-amylsalicylic acid, 3-cyclohexylsalicylic acid, 5-cyclohexylsalicylic acid, 3-methyl-5-isoamylsalicyclic acid, etc.

As the metals which form the metal compound of the aromatic carboxylic acid used in this invention, there can be mentioned metals of Group I B of the Periodic Table as, e.g., copper and silver; metals of Group II A as, e.g., magnesium and calcium; metals of Group II B, e.g. zinc, cadmium and mercury; metals of Group III B, e.g., aluminum and gallium; metals of Group IV A, e.g., tin and lead; metals of Group VI A, e.g., chromium and molybdenum; metals of Group VII B, e.g., manganese; and metals of Group VIII such as cobalt and nickel.

Of the metals salts to be used for producing the above-described metal compound of the aromatic carboxylic acid, the chlorides, sulfates, nitrates or acetates of copper, zinc, aluminum, tin, nickel, etc. are particularly useful.

The color developer of the present invention may be provided on a support in various manners. Since the effects of the present invention are naturally produced when at least one or more of the ethers or alcohols are present in the color developer layer, the process for the production is not particularly limited. However, for the purpose of simplifying the step of preparing a coating solution containing an aromatic carboxylic acid, which is one object of the present invention, it is desirable to add at least one ether or alcohol before reacting the alkali metal salt of an aromatic carboxylic acid with the water-soluble metal salt. In addition, when a water-insoluble ether or alcohol is used, it is necessary to add it before the reaction between the alkali metal salt of the aromatic carboxylic acid and the water-soluble metal salt occurs. Furthermore, where a water-soluble high molecular weight material such as water-soluble polyvinyl alcohol, methyl cellulose, hydroxymethyl cellulose, etc. as a viscosity reducing agent, is added before the reaction between the alkali metal salt of an aromatic carboxylic acid and the water-soluble metal salt takes place, a metal compound of an aromatic carboxylic acid having low viscosity and small particle size can be produced. Of such water-soluble high molecular weight materials, partially saponified polyvinyl alcohol having polymerization degree of not more than 1000 is particularly effective.

Also, the effects of the present invention are not decreased at all even when acidic resins such as phenol-formaldehyde resins, metal oxides, metal hydroxides, clays or the chemically or physically treated embodiments thereof are incorporated in the color developer layer of the present invention.

To the coating solution, there may be added acid resins such as phenol-formaldehyde resin such as p-phenylphenol-formaldehyde resin, p-t-butylphenol-formaldehyde resin, p-chlorophenol-formaldehyde resins, other color developers such as Japanese acid clay and active clay, attapulgite, inorganic pigments such as metal oxides and metal hydroxides or chemically or physically treated-products thereof. Examples of the metal are Zn, Mg and Al.

The Japanese acid clay, active clay or attapulgite is generally used in an amount not less than 1 wt%, preferably 20 to 2000 wt%, more preferably 500 to 1000 wt% based on the metal compound of aromatic carboxylic acid, and the metal oxide or hydroxide is generally used in an amount of from about 20 to 400 wt%, preferably 50 to 200 wt% based on the metal compound of aromatic carboxylic acid.

In applying the coating solution of the invention to a support such as paper, synthetic paper, synthetic resin film, etc., there can be used, if necessary, binder material such as latexes, starches, gum arabic, carboxymethyl cellulose or casein.

The coating solution, which is prepared as described above, may contain a binder such as latex, polyvinyl alcohol, maleic anhydride-styrene copolymer, starch and gum arabic. It is to be uderstood that all binders well-known as film-forming materials can be used in the invention. The binders can be classified into three groups i.e., (1) a water soluble or hydrophilic binder, for example, a natural compound such as proteins (e.g., gelatin, gum arabic, colloid albumin, casein), celluloses (e.g., carboxymethyl cellulose, hydroxyethyl cellulose), saccharoses (e.g., agar, sodium alginate, starch, carboxymethyl starch), and a synthetic compound such as polyvinyl alcohol, poly-N-vinylpyrrolidone, polyacrylate, polyacrylamide; (2) a water-dispersible binder, for example, latex such as styrenebutadiene copolymer latex, styrene-maleic anhydride copolymer latex; and (3) an organic solvent-soluble binder such nitrocellulose, ethyl cellulose or polyester. These binders can be used in the form of solution or dispersion in a solvent in the invention, and the binder can be varied depending upon the type of the solvent. Preferably, the water-soluble or dispersible binder can be used in the aqueous solution or dispersion. Of course, the metal compound of aromatic carboxylic acid can be coated without using the binder. It is to be noted that the binder is optional because it may not be necessary in case where the solvent is organic in nature.

The amount of these binders to be used varies depending upon the kind thereof and the kind of additives used, but an amount of from 5 to 30 parts by weight per 100 parts by weight of solid ingredients contained in the coating solution generally is desirable.

The coating solution is applied to the support in general a minimum about of 0.1 g/m.sup.2 as the metal compound of the aromatic carboxylic acid. Generally from about 0.1 to 10 g/m.sup.2 preferably from 0.2 to 5 g/m.sup.2, is suitable. The upper limit of the coating amount is determined only by economic reasons, and the effects of the present invention are not dissipated even when a coating amount above the above-described range is used. In addition, the recording sheet of the present invention may assume any form known in the art. For example, the color developer and color former may be provided on the same surface or opposite surfaces of a support, or on different supports.

Since the recording sheet of the present invention is characterized by the color developer, various conditions other than the aforesaid conditions, i.e., various optional additives to the color developer layer, the procedure of addition, the kind and form of color former which couples with the developer and the kind of solvent used, may be selected with ease based on common knowledge in the art.

According to the present invention, the color-developing ability is markedly improved, the step for preparing a coating solution is simplified, and a coating solution having low viscosity and excellent coating characteristics are produced. As used herein the nature of the low viscosity is a viscosity of the coating solution such that the coating amount is not more than 5 g/m.sup.2 when the coating solution is coated on a support using air knife coating of which air knife pressure is 2000 mmH.sub.2 O and of which coating speed is 400 m/min.

The recording sheet of the present invention will now be described in the greater detail below by reference to the following examples. These examples are given for the purposes of illustration and are not to be interpreted as limiting the invention.

Additionally, the effects in examples were confirmed using the combination of an upper sheet and a lower sheet, the upper sheet being prepared by producing color former-containing microcapsules in the following manner and applying them to a support, and the lower sheet being prepared by applying a color developer of the present invention to a support.

Microcapsules containing a color former can be produced by various known processes. Typical of the capsule formation methods are those utilizing the coacervation of a hydrophilic colloid sol as described in U.S. Pat. Nos. 2,800,457, 2,800,458, and typical of those utilizing interfacial polymerization are those described in British Pat. Nos. 867,797, 950,443, 989,264 and 1,091,076. The color former is dissolved in a solvent and then in microencapsulated.

Representative of the many solvents which can be used are one or more of the natural or synthetic oils, for example, chlorinated biphenyls, chlorinated terphenyls, alkylated biphenyls, alkylated terphenyls, chlorinated paraffins, chlorinated naphthalenes, alkylated naphthalenes, kerosine, paraffin, naphthene oils and cotton seed oil.

In the practice of the invention the color former (which is an electron donating colorless organic compound capable of forming a distinct color when contacted with an electron accepting acid compound) is not particularly limited but examples thereof are: triarylmethane type compounds such as 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, i.e., crystal violet lactone (which will hereinafter be referred to as "CVL"), 3,3-bis-(p-dimethylaminophenyl)phthalide, 3-(p-dimethylaminophenyl)-3-(1,2-dimethylindole-3-yl)phthalide, 3-(p-dimethylaminophenyl)-3-(2-methylindole-3-yl)phthalide, 3-(p-dimethylaminophenyl)-3-(2-phenylindole-3-yl)phthalide, 3,3-bis(1,2-dimethylindole-3-yl)-5-dimethylaminophthalide, 3,3-bis(1,2-dimethylindole-3-yl)-6-dimethylaminophthalide, 3,3-bis(9-ethylcarbazole-3-yl)-5-dimethylaminophthalide, 3,3-bis(2-phenylindole-3-yl)-5-dimethyl-aminophthalide and 3-p-dimethylaminophenyl-3-(1-methylpyrrole-2-yl)-6-dimethylaminophthalide, diphenylmethane type compounds such as 4,4'-bis-dimethylaminobenzhydrinbenzyl ether, N-halophenyl-leuco auramine and N-2,4,5-trichlorophenyl leuco auramine, xanthen type compounds such as rhodamine B-anilinolactam, rhodamine B-p-nitroanilinolactam, rhodamine B-p-chloroanilinolactam, 7-dimethylamino-2-methoxyfluoran, 7-diethylamino-2-methoxyfluoran, 7-diethylamino-3-methoxyfluoran, 7-diethyl-amino-3-chlorofluoran, 7-diethylamino-3-chloro-2-methylfluoran, 7-diethylamino-2,3-dimethylfluoran, 7-diethylamino-3-acetylmethylaminofluoran, 7-diethylamino-3'-methylaminofluoran, 3,7-diethylaminofluoran, 7-diethylamino-3-dibenzylaminofluoran, 7-diethylamino-3-methylbenzylaminofluoran, 7-diethylamino-3-chloroethylmethylaminofluoran and 7-diethylamino-3-diethylaminofluoran, thiazine type compounds such as benzoyl leuco methylene blue and p-nitrobenzyl leuco methylene blue, spiro compounds such as 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3,3'-dichloro-spiro-dinaphthopyran, 3-benzylspirodinaphthopyran, 3-methylnaphtho-(3-methoxy-benzo)-spiro-pyran and 3-propyl-spiro-dibenzopyran.

Coating may be carried out by any coating system, such as, air knife coating, blade coating, roll coating or by any known printing system. In the Examples, the microcapsules were produced as follows according to U.S. Pat. No. 2,800,457.

Hereinafter, all "percents" and "parts" are by weight.

10 Parts of acid-processed pigskin gelatin and 10 parts of gum arabic were dissolved in 400 parts of water at 40.degree.C, and 0.2 part of Turkey red oil was added thereto as an emulsifier. Then, 50 parts of a color former oil was emulsified and dispersed therein. The color former oil was prepared by dissolving 2% of crystal violet lactone or 3-N,N-diethylamino-7-N,N-dibenzylaminofluoran in an oil comprising 4 parts of chlorinated diphenyl and 1 part of kerosene. The emulsification was discontinued when the average size of the oil droplets became 5 microns. To this was added water at 40.degree.C to make a total of 900 parts while continuing the stirring. At this time, care was taken so that the liquid temperature did not become lower than 40.degree.C. Subsequently, 10% acetic acid was added thereto, and the pH of the solution was adjusted to 4.0-4.2 to cause coacervation. The stirring was further continued and, after 20 minutes elapsed, the coacervate film deposited around the oil droplets was gelled by cooling with ice-water. When the liquid temperature reached 20.degree.C, 7 parts of 37% formalin was added thereto. When the temperature reached 10.degree.C, a 15% sodium hydroxide aqueous solution was added thereto to adjust the pH to 9. Subsequently, the system was heated for 20 minutes under stirring to raise the liquid temperature to 50.degree.C.

The thus obtained microcapsule dispersion was adjusted to 30.degree.C and applied to a 40 g/m.sup.2 paper in an amount of 6 g/m.sup.2 based on the amount of solid ingredients followed by drying.

The following examples and comparative examples were conducted using a sheet coated with microcapsules containing crystal violet lactone or 3-N,N-diethylamino-7-N,N-dibenzylaminofluoran.

EXAMPLE 1

0.1 Mol of 5-tert-butylsalicylic acid was dissolved in a mixture of 0.1 mol of sodium hydroxide and 300 ml of water. To this solution were added 30 g of a 10% polyvinyl alcohol (polymerization degree: about 500; saponification degree: about 87%) aqueous solution and an ether or alcohol as listed in the following table. Then, a solution prepared by dissolving 0.1 mol of zinc chloride in 100 cc of water was gradually added thereto under stirring. The resulting coating solution was coated on a 50 g/m.sup.2 paper in an amount of 2 g/m.sup.2 based on the solid ingredients followed by drying. The viscosity of the coating solution was low, and the coating characteristics of the solution were good.

COMPARATIVE EXAMPLE 1

0.1 Mol of 5-tert-butylsalicylic acid was dissolved in a mixture of 0.1 mol of sodium hydroxide and 300 ml of water. To this solution was added 30 g of a 10% polyvinyl alcohol (as described above) aqueous solution. Then, a solution prepared by dissolving 0.1 mol of zinc chloride in 100 cc of water was gradually added thereto. Since the resulting coating solution contained coagulated material, ultrasonic waves were applied thereto to make the coagulated material fine. Thereafter, the coating solution was coated on a 50 g/m.sup.2 paper in an amount of 2 g/m.sup.2 on a solids basis, followed by drying.

Results of Comparison Test __________________________________________________________________________ No. Kind Ether or Amount Color-developing* Color-develop- Alcohol Added Ability Toward ing*Ability Crystal Violet Toward 3-N,N- Lactone diethylamino-6, 8-diethylfluoran __________________________________________________________________________ 1 Com- parative -- -- 0.731 0.602 Ex. 1 2 Ex. 1 Butanol 15 g 0.873 0.710 3 Ex. 1 Diethylene Glycol 20 g 0.935 0.757 Monobutyl Ether 4. Ex. 1 Ethylene Glycol 30 g 0.952 0.783 Monobutyl Ether 5 Ex. 1 3-Methoxy- butyl 20 g 0.894 0.720 Acetate 6 Ex. 1 Diethylene Glycol 20 g 0.855 0.698 Monomethyl Ether __________________________________________________________________________ *In the examples the color developing ability was determined by an optica densitometer (reflectance at 400 to 700 m.mu.). The numerical value shows the color density at maximum.

EXAMPLE 2

0.1 Mol of 5-tert-butylsalicylic acid was dissolved in a mixture of 0.1 mol of sodium hydroxide and 300 ml of water. To this solution were added 30 g of a 10% polyvinyl alcohol (as described in Example 1) aqueous solution, 10 g of diethylene glycol monobutyl ether and 10 g of talc. Then, a solution prepared by dissolving 0.7 mol of zinc chloride in 100 cc of water and a solution prepared by dissolving 0.3 mol of nickel sulfate in 300 cc of water were gradually added thereto under stirring. To this solution was added 20 g of a styrene-methyl methacrylate (1:1 molar ratio) copolymer latex to prepare a coating solution. The resulting solution was applied to a 50 g/m.sup.2 paper in an amount of 3 g/m.sup.2 based on the solid ingredients followed by drying. The viscosity of the solution was low, and the coating characteristics of the solution were good.

COMPARATIVE EXAMPLE 2

0.1 Mol of 5-tert-butylsalicylic acid was dissolved in 0.1 mol of caustic soda and 300 ml of water. To this solution was added 30 g of a 10% polyvinyl alcohol aqueous solution. Then, a solution prepared by dissolving 0.7 mol of zinc chloride in 700 cc of water and a solution prepared by dissolving in 300 cc of water 0.3 mol of nickel sulfate were gradually added thereto under stirring. To this solution was added 20 g of a styrene-methyl methacrylate copolymer latex to prepare a coating solution.

Since the viscosity of the coating solution increased, many bubbles were contained therein, and since the size of the particles became large, ultrasonic waves were applied to the soluton. The solution was then coated on a 50 g/m.sup.2 paper in an amount of 3 g/m.sup.2 on a solids basis, followed by drying.

Results of Comparison Test __________________________________________________________________________ Run Kind Ether Amount Color-developing Color-developing No. Added Ability Toward Ability Toward Crystal Violet 3-N,N-Diethyl- Lactone amino-7-N,N- dibenzylamino- fluoran __________________________________________________________________________ 7 Com- parative -- -- 0.753 0.611 Ex. 2 8 Ex. 2 Diethylene 30 g 0.895 0.713 Glycol Mono Butyl Ether __________________________________________________________________________

EXAMPLE 3

0.1 Mol of 3,5-di-tert-butylsalicylic acid was dissolved in a mixture of 0.1 mol of sodium hydroxide and 300 ml of water. To this solution were added 50 g of a 10% polyvinyl alcohol (as described in Example 1) aqueous solution, 20 g of agalmatolite and an ether or alcohol as shown in the following table. Then, a solution prepared by dissolving 0.15 mol of zinc chloride in 1000 ml of water was gradually added thereto under stirring. Furthermore, 50 g of a styrene-butadiene copolymer latex was added thereto. The resulting coating solution was applied to a 50 g/m.sup.2 paper in an amount of 3 g/m.sup.2 on a solids basis. The viscosity of the solution was low, and the coating characteristics of the solution were good.

COMPARATIVE EXAMPLE 3

0.1 Mol of 3,5-di-tert-butysalicylic acid was dissolved in a mixture of 0.1 mol of sodium hydroxide and 300 ml of water. To this solution were added 50 g of a 10% polyvinyl alcohol (as described in Example 1) aqueous solution and 20 g of agalmatolite. Then, a solution prepared by dissolving 0.15 mol of zinc chloride in 1000 ml of water was gradually added thereto under stirring. Furthermore, 50 g of a styrene-butadiene copolymer latex was added thereto. The resulting coating solution was applied to a 50 g/m.sup.2 paper in an amount of 3 g/m.sup.2 on a solids basis. The coating solution had a high viscosity and contained many bubbles, and the particle size of the metal compound was large. Therefore, the solution was coated on the support after applying ultrasonic waves thereto.

Results of Comparison Test __________________________________________________________________________ Run Kind Ether or Amount Color-developing Color-developing No. Alcohol Added Ability Toward Ability Toward 3- Crystal Violet N,N-Diethylamino- Lactone 7-N,N-dibenzyl- aminofluoran __________________________________________________________________________ 9 Com- parative -- -- 0.761 0.655 Ex. 1 10 Ex. 3 sec-Butyl 10 g 0.867 0.713 Alcohol 11 Ex. 3 n-Nonyl 10 g 0.798 0.677 Alcohol 12 Ex. 3 Ethylene 10 g 0.896 0.720 Glycol Di- methyl Ether 13 Ex. 3 Polyoxy- 10 g 0.790 0.684 ethylene Oleyl Alcohol Ether (22 ethenoxy units) __________________________________________________________________________

EXAMPLE 4

5 Grams of activated clay was dispersed in 50 cc of water. To this was added 0.6 cc of a 20% sodium hydroxide. Then, a solution prepared by dissolving 10 g of a 10% polyvinyl alcohol (as described in Example 1) aqueous solution and 0.012 mol of zinc sulfate in 10 cc of water was gradually added thereto under stirring. Furthermore, after adding thereto an alcohol given in the following table, a solution prepared by dissolving 0.01 mol of 3,5-di-tert-butylsalicylic acid and 0.01 mol of sodium hydroxide in 30 cc of water was gradually added thereto. After the completion of the addition, 4 g of a styrene-butadiene latex was added thereto to prepare a coating solution. The resulting coating solution was coated onto a 50 g/m.sup.2 paper in an amount of 3 g/m.sup.2 on a solids basis followed by drying.

COMPARATIVE EXAMPLE 4

5 Grams of activated clay was dispersed in 50 cc of water. To this was added 0.6 cc of 20% sodium hydroxide. Then, a solution prepared by dissolving 10 g of a 10% polyvinyl alcohol (as described in Example 1) aqueous solution and 0.012 mol of zinc sulfate in 10 cc of water was gradually added thereto under stirring. Furthermore, a solution prepared by dissolving 0.01 mol of 3,5-di-tert-butyl-salicylic acid and 0.01 mol of sodium hydroxide in 30 cc of water was gradually added thereto under stirring. After the completion of the addition, 4 g of a styrene-butadiene latex was added thereto to prepare a coating solution. The resulting coating solution was coated on a 50 g/m.sup.2 paper in an amount of 3 g/m.sup.2 on a solids basis followed by drying.

Results of Comparison Test __________________________________________________________________________ Run Kind Alcohol Amount Color-developing Color-develop- No. Added Ability Toward ing Ability Crystal Violet Toward 3-N,N- Lactone Diethylamino- 7-N,N-dibenzyl- amino fluoran __________________________________________________________________________ 14 Com- parative Ex. 4 -- -- 0.745 0.615 15 Ex. 4 n-Butyl Alcohol 0.5 g 0.852 0.701 16 Ex. 4 do. 2.0 g 0.898 0.718 17 Ex. 4 n-Hexyl Alcohol 0.5 g 0.753 0.656 18 Ex. 4 Diacetone Alcohol 1.0 g 0.887 0.711 19 Ex. 4 n-Octyl Alcohol 0.5 g 0.766 0.662 20 Ex. 4 do. 3.0 g 0.895 0.720 __________________________________________________________________________

Additionally, the coating solution of the present invention was low in viscosity and the particle size of the metal salt of the aromatic carboxylic acid formed by the reaction was small. In addition, water-immersion coloration was particularly small when n-octyl alcohol or n-hexyl alcohol was used. However, n-butyl alcohol and diacetone alcohol also provided sufficient effects.

EXAMPLE 5

5 Grams of kaolin was dispersed in 50 cc of water. To this was added under stirring a solution prepared by dissolving 10 g of a 5% hydroxymethyl cellulose and 0.01 mol of tin sulfate in 10 cc of water. Furthermore, after adding thereto 3 g of diethylene glycol monobutyl ether, a solution prepared by dissolving 0.01 mol of 3,5-di-tert-amylsalicylic acid and 0.01 mol of potassium hydroxide in 30 cc of water was gradually added thereto under stirring. After the completion of the addition, 3 g of a vinyl acetate-acrylate copolymer was added thereto to prepare a coating solution. The resulting coating solution was applied to a 50 g/m.sup.2 paper in an amount of 4 g/m.sup.2 as solids, followed by drying.

COMPARATIVE EXAMPLE 5

5 Grams of kaolin was dispersed in 50 cc of water. To this was added under stirring a solution prepared by dissolving 10 g of 5% hydroxymethyl cellulose and 0.01 mol of tin sulfate in 10 cc of water. Furthermore, 0.01 mol of 3,5-di-tert-amylsalicylic acid and 0.01 mol of potassium hydroxide were dissolved in 30 cc of water and gradually added thereto. After the completion of the addition, 4.3 g of vinyl acetate-acrylate (1:1 molar ratio) copolymer was added thereto to prepare a coating solution. The resulting coating solution was applied to a 50 g/m.sup.2 paper in an amount of 4 g/m.sup.2 on a solids basis, followed by drying.

Results of Comparison Test 5 ______________________________________ Run Kind Color-developing Color-developing No. Ability Toward Ability Toward Crystal Violet 3-N,N-Diethylamino- Lactone N,N-dibenzylamino- fluoran ______________________________________ 21 Comparative 0.750 0.618 Example 5 22 Example 5 0.902 0.727 ______________________________________

EXAMPLE 6

The procedures described in Example 1 were repeated except for adding 2 g of diethylene glycol monobutyl ether and 0.5 g of n-octyl alcohol in place of 3 g of diethylene glycol monobutyl ether. Thus, there were obtained the following results.

______________________________________ Color-developing Ability Color-developing Ability Toward Crystal Violet Toward 3-N,N-Diethylamino- Lactone 7-N,N-dibenzylaminofluoran ______________________________________ 0.900 0.723 ______________________________________

Also, the water-immersion coloration was sufficiently low. Thus, the resulting sheet was found to be a practical recording sheet.

From the results of the above-described test, it has been found that the color-developing ability toward crystal violet lactone and 3-N,N-diethylamino-7-N,N-dibenzylaminofluoran is markedly improved by adding at least one of an ether or alcohol to a color developer layer containing a metal compound of an aromatic carboxylic acid. Similar effects also were observed with respect to other color formers.

The step for preparing a coating solution was simplified and, in addition, the viscosity of the coating solution was so low that the coating solution had excellent coating characteristics.

The water-immersion coloration was also remarkably depressed and the commercial value of the resulting sheet was markedly improved. Additionally, the light fastness, and water resistance of the color image, the activity of the color developer sheet with the passage of time, and the like were not affected at all.

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

Claims

What is claimed is:

1. A recording sheet comprising a support having thereon a color developer layer capable of reacting with a color former to form color images, said color developer layer containing (1) a metal salt of an aromatic carboxylic acid and (2) at least one member selected from the group consisting of ethers and alcohols, said component (1) and said component (2) being present at a proportion sufficient to increase the color-developing ability of said color developer and said color former.

2. The recording sheet of claim 1, wherein said metal of said metal salt of an aromatic carboxylic acid is a member of Group I B, Group II A, Group II B, Group III B, Group IV A, Group VI A, Group VII B or Group VIII of the Periodic Table.

3. The recording sheet of claim 1, wherein said aromatic carboxylic acid is represented by the formula: ##SPC5##

wherein R may be the same or different and represents a hydrogen atom, a hydroxy group, a halogen atom, a nitro group, an alkyl group having 1 to 10 carbon atoms, the total carbon number in the R's being less than 13, an aryl group, an arylamino group or an alicyclic group, m is an integer of 0 to 7 and n is an integer of 0 to 5, or said aromatic carboxylic acid may be dimerized through the substituent R as a methylene group.

4. The recording sheet of claim 3, wherein said metal of said metal salt of an aromatic carboxylic acid is a member of Group I B, Group II A, Group II B, Group III B, Group IV A, Group VI A, Group VII B or Group VIII of the Periodic Table;

wherein said color developer layer contains from 10 to 250 parts by weight of said ether and alcohol per 100 parts by weight of said aromatic carboxylic acid and wherein said color developer layer is present on said support at a level of at least 0.1 g/m.sup.2 as the metal salt of the aromatic carboxylic acid;

said ether is represented by the formula:

ROX

wherein X is --(CH.sub.2).sub.p OR', --(CH.sub.2).sub.p OH, --[(CH.sub.2).sub.n O].sub.q H, --[(CH.sub.2).sub.n O].sub.q R", an alkyl group having up to 18 carbon atoms or an alkenyl group having up to 18 carbon atoms, R is an alkyl group having up to 10 carbon atoms, an aryl group having up to 10 carbon atoms or an alkenyl group having up to 10 carbon atoms, R' and R" each is an alkyl group having up to 18 carbon atoms, an aryl group having up to 18 carbon atoms or an alkenyl group having up to 18 carbon atoms, p is an integer of 1 to 20 and q is an integer of 2 to 30; and

the alcohol is an aliphatic alcohol having from 1 to 18 carbon atoms.

5. The recording sheet of claim 1, wherein said ether is a glycol ether.

6. The recording sheet of claim 1, wherein said alcohol is an alcohol having 4 or more carbon atoms.

7. The recording sheet of claim 1, wherein said color developer layer contains a mixture of at least on ether and at least on alcohol.

8. The recording sheet of claim 1, wherein said color developer layer contains from 10 to 250 parts by weight of said ether and alcohol per 100 parts by weight of said aromatic carboxylic acid and wherein said color developer layer is present on said support a level of at least 0.1 g/m.sup.2 as the metal salt of the aromatic carboxylic acid.

9. The recording sheet of claim 1, wherein said ether is represented by the formula:

ROX

wherein X is --(CH.sub.2).sub.p OR', --(CH.sub.2).sub.p OH, --[(CH.sub.2).sub.n O].sub.q H, --[(CH.sub.2).sub.n O].sub.q R", an alkyl group having up to 18 carbon atoms or an alkenyl group having up to 18 carbon atoms, R is an alkyl group having up to 10 carbon atoms, an aryl group having up to 10 carbon atoms or an alkenyl group having up to 10 carbon atoms, R' and R" each is an alkyl group having up to 18 carbon atoms, an aryl group having up to 18 carbon atoms or an alkenyl group having up to 18 carbon atoms, p is an integer of 1 to 20 and q is an integer of 2 to 30.

10. The recording sheet of claim 1 wherein said alcohol is an aliphatic alcohol having 1 to 18 carbon atoms.

11. The recording sheet of claim 1 wherein said alcohol is selected from the group consisting of n-butyl alcohol, n-amyl alcohol, n-hexyl alcohol, n-heptyl alcohol, n-octyl alcohol, n-nonyl alcohol, n-decyl alcohol, lauryl alcohol, myristyl alcohol, cetyl alcohol, stearyl alcohol, isobutyl alcohol, sec-butyl alcohol, isoamyl alcohol, tert-butyl alcohol, sec-butyl carbinol, diethyl carbinol, 1-hexanol, 2-hexanol, 3-hexanol, cyclohexanol, 3-methyl-1-pentanol, 4-methyl-2-hexanol, allyl alcohol, trans-crotyl alcohol, ciscrotyl alcohol, 2-methyl-3-buten-1-ol, o-tolyl carbinol m-tolyl carbinol, p-tolyl carbinol and benzyl alcohol.

12. The recording sheet of claim 1 wherein said aromatic carboxylic acid is selected from the group consisting of benzoic acid, nitrobenzoic acid, chlorobenzoic acid, toluic acid, 4-methyl-3-nitrobenzoic acid, 2-chloro-4-nitrobenzoic acid, 2,3-dichlorobenzoic acid, 4-methyl-3-nitrobenzoic acid, 4-acetylbenzoic acid, 2,4-dihydroxybenzoic acid, 2,5-dihydroxybenzoic acid, 1-napththoic acid, 2-naphthoic acid, 1-hydroxy-2-naphthoic acid, 2-hydroxy-3-naphthoic acid, 2-hydroxy-1-naphthoic acid, thiosalicyclic acid, salicylic acid, 3,5-dinitrosalicylic acid, 3-methylsalicyclic acid, 2,4-cresotinic acid, 2,5-cresotinic acid, 3-methylsalicyclic acid, 2,4-cresotinic acid, 2,5-cresotinic acid, 5-tert-butylsalicylic acid, 3-phenylsalicylic acid, 3-methyl-5-tert-butylsalicylic acid, 3,5-di-tert-butylsalicylic acid, 3,5-di-tert-amylsalicylic acid, 3-cyclohexylsalicylic acid, 5-cyclohexylsalicylic acid and 3-methyl-5-isoamylsalicylic acid.

13. The recording sheet of claim 1, wherein said metal salt of said aromatic carboxylic acid is a copper, zinc, aluminum, tin or nickel salt.

14. A pressure sensitive copying assembly comprising a color former layer on a first support and a color developer layer on a second support, said color developer layer and said color former layer being brought together at the time of pressure sensitive copying to permit color developer and color former to be brought into reactive contact to form a color image, said color developer layer containing (1) a metal salt of an aromatic carboxylic acid and (2) at least one member selected from the group consisting of ethers and alcohols, said component (1) and said component (2) being present at a porportion sufficient to increase the color-developing ability of said color developer and said color former.

15. The pressure sensitive copying assembly of claim 14 wherein said color developer layer contains from 10 to 250 parts by weight of said ether and alcohol per 100 parts by weight of said aromatic carboxylic acid and wherein said color developer layer is present on said support at a level of at least 0.1 g/m.sup.2 as the metal salt of the aromatic carboxylic acid.

16. The pressure sensitive copying assembly of claim 15, wherein said metal of said metal salt of an aromatic carboxylic acid is a member of Group I B, Group II A, Group II B, Group III B, Group IV A, Group VI A, Group VII B or Group VIII of the Periodic Table.

17. A pressure sensitive copying assembly comprising a color former layer and a color developer layer carried on the same support, said color developer layer and said color former layer being in relationship such that at the time of pressure sensitive copying, color developer and color former are brought into reactive contact to form a color image. Said color developer layer containing (1) a metal salt of an aromatic carboxylic acid and (2) at least one member selected from the group consisting of ethers and alcohols, said component (1) and said component (2) being present at a proportion sufficient to increase the color-developing ability of said color developer and said color former.

18. The pressure sensitive copying assembly of claim 17 wherein said color developer layer contains from 10 to 250 parts by weight of said ether and alcohol per 100 parts by weight of said aromatic carboxylic acid and wherein said color developer layer is present on said support at a level of at least 0.1 g/m.sup.2 as the metal salt of the aromatic carboxylic acid.

19. The pressure sensitive copying assembly of claim 18, wherein said metal of said metal salt of an aromatic carboxylic acid is a member of Group I B, Group II A, Group II B, Group III B, Group IV A, Group VI A, Group VII B or Group VIII of the Periodic Table.