GB2099471A - Pressure-sensitive recording material - Google Patents

Abstract

Pressure-sensitive recording material comprises a paper sheet having a surface pH of at least 6.0 and having coated thereon microcapsules containing a solution of a benzhydrylsulfone color former preferably of general formula: <IMAGE> where R1 is a monovalent aliphatic or aromatic group containing 5 to 25 C atoms and R2 is a C 1 to 5 alkyl group. Other color farmers can be included in the microcapsules, e.g. a triarylmethane. Preferred color developers are clays. The use of this color former gives good color formation without coloration of the surface of the paper or staining of cut paper edges.

Description

SPECIFICATION Pressure-sensitive recording material This invention relates to a recording material and, more particularly, to a pressure-sensitive recording material which is improved to be resistant to stain of coated surface thereof, stain of cut section thereof, and coloration of base paper surface.

It has long been known to obtain color images by contact reaction between an electron-donating or proton-accepting colorless organic compound (hereinafter referred to as a color former) and an electron-accepting or proton-donating solid acid (hereinafter referred to as a color developer). Examples of specifically utilizing this phenomenon are pressure-sensitive copying (or recording) papers (for example, U.S. Patents 2,505,470, 2,505,489, 2,550,471, 2,548,366, 2,712,507, 2,730,456, 2,730,457, 3,41 8,250 and 3,672,935) and heat-sensitive recording papers (for example, Japanese Patent Publication Nos. 4160/68, 7600/68, 14039/70, U.S. Patent 2,939,009).

Further, a printing method is known which comprises supplying a color former-containing ink to a color developer-coated sheet to obtain colored images (German Patent OLS 1,939,962).

As color developers having the above-defined properties, examples are acid clay, phenol resins and aromatic carboxylic acid metal salts.

As the color former, there have been used those which are usually colorless, which possess a partial skeleton of lactone, lactam, sultone, spyropyran, ester or amido, and which undergo ring cleavage or splitting of said partial skeleton when contacted with a color developer. Suitable color formers are Crystal violet lactone, i.e. 3,3-bis-(p-dimethylaminophenyl)-6-dimethylaminophthalide; "Crystal" is a registered Trade Mark, xanthene compounds such as rhodamine B anilinolactam, spyropyran compounds such as 3-methyl-spiro-dinaphthopyran, thiazine compounds such as benzoyl leucomethylene blue, and Ieucoauramine compounds such as N-(o-chlorophenyl)leucoauramine.

However, colored products formed by the reaction between a color former such as a triarylmethane compound, xanthene compound or spiro compound and an acid clay have poor durability, and, when in contact with water or an organic solvent, undergo reduction in density of color or disappearance of color. Of organic solvents, polar solvents such as alcohols (e.g., ethanol, butanol, propylene glycol or glycerin), amines (e.g., monoethanolamine or triethanolamine) and esters and ethers (e.g., ethyl acetate, diethylene glycol, monomethyl ether, dioctyl phthalate or dibutyl phthalate) exert strong effects on colored products when the organic solvents are contacted, directly or as a vapor, with the colored products, resulting in reduction in color density or the total disappearance of color.

The inventors have formerly proposed to use benzhydrylsulfone type color formers so as to overcome the above-described defects. However, recording sheets having coated thereon microcapsules containing this benzhydrylsulfone type color former have the defect that the coated surface becomes bluish or that a cut section thereof undergoes color staining.

Further, when this microcapsule-coated paper is used in a so-called spot-printing process, which comprises printing a color developer-containing ink onto portions where copying (or recording) is necessary, some colored products are formed on the base paper surface other than the color developercoated portions (hereinafter this is referred to as base paper coloration). Thus, elimination of these defects has been eagerly desired.

An object of the present invention is to provide a recording material which overcomes the abovedescribed defects.

It has now been found that the above-described object can be attained by coating microcapsules containing a benzhydrylsulfone color former solution onto a base paper having a surface pH of at least 6.0, preferably a surface pH of 6.0 to 8.0.

As the benzhydrylsulfone color former used in the present invention, those compounds which are represented by formula (I) are preferable:

In formula (I), R, represents a monovalent group containing from 5 to 25 carbon atoms, and R2 represents an alkyl group containing from 1 to 5 carbon atoms.

In formula (I), the monovalent group represented by R1 is preferably an alkyl group containing from 6 to 20 carbon atoms, a cycloalkyl group containing from 5 to 1 6 carbon atoms, an aralkyl group containing from 7 to 20 carbon atoms, an alkyl-substituted aryl group containing a total of from 11 to 25 carbon atoms, an acylamino-substituted aryl group containing a total of from 12 to 25 carbon atoms, an alkoxy-substituted aryl group containing a total of from 10 to 25 carbon atoms, an acyloxysubstituted aryl group containing a total of from 10 to 25 carbon atoms, an aryloxy-substituted aryl group containing a total of from 12 to 25 carbon atoms, or an aralkyl-substituted aryl group containing a total of from 13 to 25 carbon atoms, with an alkyl-substituted aryl group containing a total of from 14 to 25 carbon atoms or an alkoxy-substituted aryl group containing a total of from 12 to 25 carbon atoms being particularly preferable. As the alkyl group represented by R2 containing from 1 to 5 carbon atoms a methyl group, an ethyl group, a propyl group and a butyl group are preferable, with a methyl group being particularly preferable. Benzhydrylsulfone compounds are disclosed in U.S. Patents 3,193,404,3,278,327, etc. However, the object of the present invention is attained only by combining the benzhydrylsulfone compounds with a base paper having a surface pH of at least 6.0.

Specific examples of the compounds represented by formula (I) illustrated below: (4,4'-Bis-dimethyla mino)diphenylmethyl-n-octylsu Ifone; (4,4'-Bis-dimethylamino)diphenyl methyl-n-dodecylsulfone; (4,4'-Bis-dimethylamino)diphenylmethyl-n-hexadecylsu Ifone; (4,4'-Bis-dimethylamino)diphenylmethyl-n-octadecylsu Ifone; (4,4'-Bis-dimethyla mino)diphenyl methyl-cyclohexylsulfone; (4,4'-Bis-dimethylamino)diphenylmethyl-methylcyclohexylsulfone; (4,4'-Bis-dimethylamino)diphenylmethyl-dimethylcyclohexylsulfone; (4,4'-Bis-dimethylamino)diphenylmethyl-benzylsulfone; (4,4'-Bis-dimethylamino)diphenylmethyl-2-phenethylsulfone; (4,4'-Bis-dimethyla mino)diphenylmethyl-3-phenylpropylsulfone; (4,4'-Bis-dimethyla mino)diphenylmethyl-a'-methylbenzylsu Ifone;; (4,4'-Bis-dimethyla mino)diphenyl methyl-p-octylbenzylsulfone; (4,4'-Bis-dimethylamino)diphenylmethyl-p-dodecylbenzylsulfone; (4,4'-Bis-dimethyla mino)diphenyl methyl-n-amylphenylsulfone; (4,4'-Bis-dimethylamino)diphenylmethyl-tert-amylphenylsulfone; (4A'-Bis-dimethyIarnino)diphenylmethyliisoprnpylphenyIsuIfone; (4,4'-Bis-dimethylamino)diphenylmethyl-triisopropylphenylsu Ifone; (4,4'-Bis-dimethylamino)diphenylmethyl-di-tert-butylphenylsulfone:: (4,4'-Bis-dimethylamino)diphenylmethyl-octylphenylsulfone; (4,4'-Bis-dimethylamino)diphenylmethyl-nonylphenylsulfone; (4,4'-Bis-dimethyla mino)diphenylmethyl-dodecylphenylsu Ifone; (4,4'-Bis-dimethylamino)diphenylmethyl-tetrahydronapthylsulfone; (4,4'-Bis-dimethylamino)diphenylmethyl-isopropyl naphthylsulfone; (4,4'-Bis-dimethyla mino)diphenylmethyl-diisopropylnaphthylsulfone; (4,4'-Bis-dimethylamino)diphenylmethyl-cycloheXylphenylsu If one; (4,4'-Bis-dimethyla mi no)diphenylmethyl-a-methylbenzylphenylsulfone; (4,4'-Bis-dimethylamino)diphenylmethyl-diphenylmethylphenylsulfone; (4,4'-Bis-dimethyla mino)diphenylmethyl-benzylphenylsu Ifone; (4,4'-Bis-dimethylamino)diphenylmethyl-phenoxyphenylsulfone; (4,4'-Bis-dimethyla mino)diphenylmethyl-octyloxyphenylsu Ifone; (4,4'-Bis-dimethylamino)diphenylmethyl-dodecyloxyphenylsulfone;; (4,4'-Bis-dimethylamino)diphenylmethyl-octanoylaminophenylsulfone; (4,4'-Bis-dimethyla mino)diphenylmethyl-n-dodecylsulfone; (4,4'-Bis-dibutylamino)diphenylmethyl-benzylsu Ifone; (4,4'-Bis-dimethyla mino)diphenylmethyl-dodecanoylaminophenylsulfone; and (4,4'-Bis-dimethylamino)diphenyl methyl-dodecanoyloxyphenylsulfone.

These benzhydrylsulfone compounds can be used in combination with other color formers. In particular, when Crystal violet lactone is used as the other color former in combination with these benzhydrylsulfone compounds of 10 to 200% by weight, preferably 50 to 100% by weight, based on the weight of Crystal violet lactone, they provide colored products having improved durability and prevent base paper coloration, and thus such a combination is most preferable.

Examples of other coior formers include triarylmethane compounds, xanthene compounds, spiro compounds and thiazine compounds.

As a base paper on which a microcapsule dispersion is to be coated, rosin-sized papers can be used. Such rosin-sized papers conventionally contain alumina sulfate, and have a surface pH of from about 3 to 5.

In the present invention, so-called neutrally sized paper containing no alumina sulfate and having a surface pH of at least 6.0, preferably 6.0 to 8.0 is used. The surface pH can easily be measured by coating a pH indicator on a base paper. For example, a paper surface pH-testing solution made by Kyoritsu Rikagaku Kenkyusho K.K. can be utilized.

In the present invention, solvents for dissolving the benzhydrylsulfone color formers include paraffin oil having a boiling point of 1200C or more, chlorinated paraffin (chlorination degree: about 1 5% to 60%), and alkyl or aralkyl-benzene or naphthalene (alkyl moiety containing about 5 or less carbon atoms) such as triphenyimethane, diphenyltolylmethane, xylylphenylethane, benzylxylene, amethylbenzyltoluene, diisopropylnaphthalene, isobutylbiphenyl, tetrahydronaphthalene, hydrogenated terphenyl, di-a-methylbenzylxylene, tert-butyl-diphenyl ester, styrene dimer, etc.

Microcapsules to be used in the present invention can be prepared, for example, by a process utilizing coacervation as described in U.S. Patents 2,800,457 and 2,800,458, a process of interfacial polymerization as described in British Patent 990,443 and U.S. Patent 3,287,1 54, a process of polymer precipitation as described in U.S. Patents 3,418,250 and 3,660,304 and Japanese Patent Publication No. 23165/72, and a process of reactant polymerization from inside the oil droplets as described in U.S.

Patents 3,726,804 and 3,796,669. In particular, a process for forming a capsule wall on the outside surface of the oil droplets is advantageous from the viewpoint of forming highly concentrated fine oil droplets.

The benzhydryl sulfone color former is preferably used in an amount of from 0.03 to 0.5 g/m2, and the color developer in an amount of from 0.1 to 3 g/m2.

In the present invention, particularly remarkable effects can be obtained by using acid clay and clay minerals such as bentonite and kaolin as the color developer; however, other color developers can be used. Examples of other developers include phenol resins and aromatic carboxylic acid polyvalent metal salts.

The developer may be coated on the recording material or on a separate developing sheet.

The present invention will now be described in more detail by reference to examples of preferred embodiments.

EXAMPLES Preparation of color former sheet: 10 parts of acid-processed gelatin having an isoelectric point of 8.0 and 10 parts of gum arabic were dissolved in 60.parts of 400C water, and 0.2 part of sodium alkylbenzenesulfonate was added thereto as an emulsifier, followed by adding thereto 50 parts of a 3.5% solvent solution of a color former as indicated in Table 1. Then, the resulting mixture solution was stirred to effect emulsification thereof.

Additionally, the solvent used was a mixture of diisopropylnaphthalene and a petroleum fraction boiling at from 1 400C to 1 600C (3 : 2 by volume).

When the average size of the emulsified oil droplets became 8 microns, 100 parts of a 400C water was added thereto to stop the progress of emulsification.

While continuing the stirring, 210 parts of a 300C water was added thereto, and 20% hydrochloric acid was added thereto to adjust the pH of the system to 4.4. The solution was further cooled to 80C while stirring, and then 1.5 parts of 20% glutaraldehyde was added thereto.

Subsequently, 30 parts of a 10% carboxymethyl starch solution was poured thereinto, and 25% sodium hydroxide was dropwise added thereto to adjust the pH to 8.5. Then, the solution temperature was raised to 300C to obtain microcapsules having hardened wall.

10 parts of cellulose flock was dispersed therein, followed by coating the resulting solution on a base paper as indicated in Table 1 below.

Preparation of base paper: 40 g/m2 of base paper A having a surface pH of 6.5 was obtained using a Nagatsuna paper machine with LBKP: NBKP = 8 2 and freeness of 45 SR by adding 0.2% of Aquopale 360 (alkylketene dimer; made by Hercules Company) and 2.0% cationic starch.

In the same manner as described above except for further adding 5% calcium carbonate (precipitated calcium carbonate PC: made by Shiraishi Karushiumu K.K.) upon the making of the paper A, there was prepared a 40 g/m2 of base paper B having a surface pH of 7.2.

Further, for comparison, 40 g/m2 of a base paper C having a surface pH of 3.2 was prepared by adding 1.0 wt% of rosin and 2.0 wt% of alumina sulfate in place of the Aquopale 360 and cationic starch.

Additionally, the paper surface pH was measured by using a paper surface pH-testing solution made by Kyoritsu Rikagaku Kenkyusho K.K. (Kyoritsu Physical and Chemical Research Institute).

Testing method: Two color former-containing capsule sheets were superposed on each other, and a pressure of 300 kg/cm2 was applied thereto from the base paper side. The coloration reflection density of the base paper was measured using a color analyzer Model 307 made by Hitachi Ltd.

Also, the stain density of the capsule-coated surface was similarly measured.

Further, 20 sheets of capsule-coated paper were superposed on each other, and subjected to guillotine cutting to compare color staining of the cut section. The color staining of the cut section was determined by visual observation.

Additionally, the density was measured as reflection density for 617 nm light.

TABLE 1 Color Stain Coated Coloration of Capsule- Color Stain Base of Base coated of Cut Color Former Used Paper Paper Surface Section Example 1 (4,4'-Bis-dimethylamino)- Base 0.07 0.042 almost no diphenylmethyl-p-dodecyl- Paper A coloration benzenedisulfone (pH 6.5) Example 2 (4,4'-Bis-dimethylamino)- Base 0.07 0.041 almost no diphenylmethyl-dodecyl Paper B coloration oxyphenylsulfone (pH 7.2) Example 3 a mixture (3: by wt.) of(4,4'- Base 0.06 0.040 almost no bis-dimethylamino)di- Paper B coloration phenylmethyl-diisopropyl- (pH 7.2) naphthylsulfone and crystal violet lactone Comparative same as in Example 1 Base 0.22 0.068 serious Example 1 Paper C coloration (pH 3.2) In Table 1, a base paper coloration density of 0.08 or less is a level considered as imposing no problems. Thus, conventional defects can be overcome by using the benzhydrylsulfone type color former and a neutrally sized base paper having a surface pH of at least 6.0.

Also, problems of color stain of capsule-coated surface and color stain of cut section can be solved by the use of neutrally sized base paper having a surface pH of at least 6.0.

On the other hand, these capsule-coated sheets show excellent color-forming characteristics when superposed under local pressure on color-developing sheets to form colors thereon. Thus, the recording materials of the present invention clearly have excellent properties.

Claims (10)

1. A pressure-sensitive recording material comprising a base paper having a surface pH of at least 6.0 and having coated thereon microcapsules containing a solution of a benzhydrylsulfone color former.

2. A pressure-sensitive recording material as claimed in Claim 1, wherein the color former is represented by the general formula (I)

wherein R, represents a monovalent group containing from 5 to 25 carbon atoms and R2 represents an alkyl group containing from 1 to 5 carbon atoms.

3. A pressure-sensitive recording material as claimed in Claim 2, wherein the monovalent group represented by R1 is an alkyl group containing from 6 to 20 carbon atoms, a cycloalkyl group containing from 5 to 1 6 carbon atoms, an aralkyl group containing from 7 to 20 carbon atoms, an alkyl-substituted aryl group containing a total of from 11 to 25 carbon atoms, an acylamino-substituted aryl group containing a total of from 12 to 25 carbon atoms, an alkoxy-substituted aryl group containing a total of from 10 to 25 carbon atoms, an acyloxy-substituted aryl group containing a total of from 10 to 25 carbon atoms, an aryloxy-substituted aryl group containing a total of from 12 to 25 carbon atoms, or an aralkyl-substituted aryl group containing a total of from 13 to 25 carbon atoms.

4. A pressure-sensitive recording material as claimed in Claim 3, wherein R, represents an alkylsubstituted aryl group containing a total of from 14 to 25 carbon atoms or an alkoxy-substituted aryl group containing a total of from 12 to 25 carbon atoms.

5. A pressure-sensitive recording material as claimed in Claims 2, 3 or 4, wherein R2 represents a methyl, ethyl, propyl or butyl group.

6. A pressure-sensitive recording material as claimed in any preceding claim, wherein the color former is present in an amount of from 0.03 to 0.5 grams per square metre.

7. A pressure-sensitive recording material as claimed in any preceding claim, wherein the microcapsules additionally contain another color former.

8. A pressu re-sensitive-recording material as claimed in any preceding claim, wherein the surface pH is 6.0 to 8.0.

9. A pressure-sensitive recording material as claimed in Claim 1, substantially as hereinbefore described in Example 1,2 or 3.

10. A method of forming a recording, which comprises applying local pressure to a sheet of recording material as claimed in any preceding claim, in contact with a color developer.