GB2034782A - Recording Materials - Google Patents

Abstract

A recording material includes a support coated with a synthetic colour developer at a coating rate not less than 0.2 g/m<2> and an inorganic pigment at a coating rate not less than 1.8 g/m<2> together with a binder, said inorganic pigment having an oil absorbance not less than 45 and a volume average particle diameter not larger than 8 microns.

Description

SPECIFICATION Recording Materials This invention relates to recording materials.

It is well known that an electron donating (or proton-accepting) color former such as Crystal Violet lactone is converted into a colored product when brought into contact with an electron accepting (or proton-donating) color developer such as acid clay, a phenolic compound, salicylic acid or benzoic acid.

Among recording materials utilizing this phenomenon, there are pressure-sensitive paper sheets as described in, 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 and 3,418,250; and Japanese Patent Applications (OPI) Nos. 28,411/1974 and 44,009/1 975; heat sensitive recording papers as described in, for example, Japanese Patent Publication No. 4160/1968 and U.S. Patent 2,939,009; and electrically conductive recording papers.

The recording material of the present invention includes all of these different types of materials.

A representative embodiment of such a recording material is one in which one surface of a sheet support is coated with microcapsules each containing an oil droplet in which a color former is dissolved, while a color developer is coated on the other surface of the same sheet. When one writes on a set of such sheets superimposed in such a manner that the two coatings are in face-to-face contact, the writing pressure causes the capsules in the inscribed area to rupture whereby the oil containing the color former is transferred to the surface coated with the color developer and reacts therewith thus giving rise to a colored image.

Another embodiment of the recording material based on the above-cited color forming mechanism is a heat-sensitive paper in which a color former and a color developer, each being in a finely-divided form, are coated on a support in such a manner that each ingredient is isolated from the other by the use of a binder. When the paper is heated, at least one of the two ingredients melts and dissolves and reacts with the other, thus forming a colored product.

A number of problems exist with conventional recording materials. They tend to yellow and the color developing power of the acid substance contained in the coating deteriorates under the influence of sunlight.

Further, when the recording sheet is subjected to printing on the surface coated with a color developer (particularly, with organic solvent soluble developers), drying of the printing ink is often slow and causes sheet soiling by the ink (ink set retardation).

Accordingly, one object of the present invention is to provide a recording material having excellent light-fastness.

Another object of the present invention is to provide a recording sheet having improved printing property.

The above-mentioned objects of the present invention have been achieved in a recording material comprising a support coated with a synthetic color developer at a coating rate not less than 0.2 g/m2 and an inorganic pigment at a coating rate not less than 1.8 g/m2 together with a binder, said inorganic pigment having an oil absorbance not less than about 45 and a volume average particle diameter not larger than about 8 microns.

Synthetic color developers used in the instant invention comprise the metal salts of aromatic and aliphatic carboxylic acids. Among such aromatic carboxylic acids, those represented by the following formula are particularly preferred.

In the formula, R1, R2, R3, R4and R5 each represents a hydrogen atom, a halogen atom, a hydroxyl group, an amino group, an alkylamino group, a nitro group, an aldehyde group, an alkyl group, a cycloalkyl group, an aryl group, an alkaryl group, an aralkyl group or an alkoxy group in which said carbon atom containing groups contain up to 18 carbon atoms. Alternatively, R, and R2, or R3 and R4 are combined to form a five or six membered saturated or unsaturated or heterocyclic ring.

Among the compounds represented by the above general formula, particularly useful are those in which at least one of R1 and R5 is a hydroxyl group and in which the o- or p-position relative to the hydroxyl group is substituted with an alkyl group, an aryl group or an aralkyl group, etc. Of these the most preferable compounds are those in which the total number of carbon atoms in R1 to R5 is 8 or more.

Examples of such aromatic carboxylic acids include the following: 2,4-dichlorobenzoic acid, p-isopropylbenzoic acid, 2,5-dinitrobenzoic acid, p-t-butylbenzoic acid, N-phenylanthranylic acid, 4-methyl-3-nitrobenzoic acid, salicylic acid, benzoic acid, naphthoic acid, phenylacetic acid, m-hydroxybenzoic acid, p-hydroxybenzoic acid, 3,5-dinitrosalicylic acid, 5-tbutylsalicylic acid, 3-phenylsalicylic acid, 3-methyl-5-t-butylsalicylic acid, 3,5-di-tert-amylsalicylic acid, 3-cyclohexylsalicylic acid, 5-cyclohexylsalicylic acid, 3-methyl-5-isoamylsalicylic acid, 5isoamylsalicylic acid, 3,5-di-sec-butylsalicylic acid, 5-nonylsalicylic acid, 2-hydroxy-3-methylbenzoic acid, 2-hydroxy-5-t-butylbenzoic acid, 2,4-cresotinic acid, 5,5-methylenedisalicylic acid, o-, m- and pacetoaminobenzoic acid, 2,4-dihydroxybenzoic acid, 2,5-dihydroxybenzoic acid, anachardic acid, 1naphthoic acid, 2-naphthoic acid, 1 -hydroxy-2-naphthoic acid, 2-hydroxy-3-naphthoic acid, 2-hydroxy1-naphthoic acid and thiosalicylic acid.

Especially suitable acids include 3,5,di(a-methylbenzyl)salicylic acid, 3-(-methyIbenzyl)-5-(a,ar- dimethylbenzyl)salicylic acid, 3-(4'- & a'-dimethylbenzyl)phenyl-5-(ar,a-dimethylbenzyl)salicylic acid, 3,5-di-t-butylsalicylic acid, 3,5-di-t-octylsalicylic acid, 3-cyclohexyl-5-(a,a-dimethylbenzyl)salicylic acid, 3-phenyl-5-(cg,-dimethylbenzyl)salicylic acid and 3,5-di(a,-dimethylbenzyl)salicylic acid.

Among the metal salts of aliphatic carboxylic acids, the metal salts of C4-C26 saturated mono- or polybasic aliphatic acids and of C10-C24 unsaturated mono- or dibasic aliphatic acids are preferred.

Branched chain aliphatic acids associated with the above-cited compounds may also be used.

Practical examples for the saturated aliphatic carboxylic acid include n-butyric acid, tartaric acid, isovaleric acid, caproic acid, sebacic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, lignoceric acid and cerotic acid. Further, branched chain aliphatic acids include hydrocalvic acid and cholic acid. Suitable unsaturated aliphatic acids and fatty acids include A9'10-decyleic acid, phenoxyacetic acid, A9 10-dodecycleic acid, palmitoleic acid, oleic acid, ricinoleic acid, petrocelic acid, vaccenic acid, linoleic acid, linolenic acid, eleostearic acid, licanic acid, valinalic acid, talylic acid, gadoleic acid, arachidonic acid, cetoleic acid, erucic acid and seracholeic acid.

Metals which form salts with the above-cited aliphatic and aromatic carboxylic acids include, Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, K, Ge, Sr, Y, Zr, Mo, Ag, Cd, In, Sn, Sb, Ba, W, Pb, Bi and Na.

Among these metals, particularly effective are Zn, Sn, Al, Mg, Ca, Na and K.

The inorganic pigments include those of natural and synthetic origin, including, precipitated barium sulfate, barium carbonate, calcium carbonate powder, precipitated calcium carbonate, asbestos, clay, pulverized silica, silicic acid powder, diatomaceous earth, talc, basic magnesium carbonate, alumina white, gross white, satin white, zinc oxide (zinc white), white lead, basic lead sulfate, lead sulfate, lithopone, zinc sulfide, titanium dioxide, antimony oxide, baryta, mica, yellow earth, calcium silicate, synthetic calcium carbonate and magnesium carbonate. Among these zinc oxide is preferred. However, it should be noted that not all of these inorganic pigments are suited for the present invention but that for the present purpose those with an oil absorbance not less than about 45 and particle size not exceeding about 8 microns are required.A certain inorganic pigment (e.g., clay) defined by its chemical composition differs in oil absorbance as well as particle size depending on its origin, the method of preparation etc. Accordingly, the inorganic pigment claimed in the instant invention is such as to have an oil absorbance not less than about 45 and an average particle size not exceeding 8 microns.

In general, inorganic pigments with an oil absorbance not less than about 45 and preferably used in the instant invention can be obtained by subjecting ordinary pigments to a suitable chemical treatment such as with acids, alkalis or with organic solvents including octanol under the application of heat, or to a physical treatment such as heating or grinding but generally the above pigments can be found in a commercial form having the required oil absorbance.

The oil absorbance of an inorganic pigment can be determined in the following manner: From 1 to 5 g of the pigment is placed on a glass plate with the dimensions of about 250x250x 5 mm, onto which diisopropylnaphthalene (available from Kureha Chemical Co., under the tradename of KMC-F1 13) is dropped gradually from a burette. With the addition of each drop, the sample is kneaded with a spatula. Finally the entire amount of the sample, originally in a powder form, gradually forms a lump. The amount of diisopropylnaphthalene required to achieve such lump formation is measured and the oil absorbance is calculated by the following formula.

amount of diisopropylnaphthalene (g) oil absorbance= x100 amount of sample (g) Binder materials can be selected by considering the adhesion of the resulting recording layer to the support, the film strength of the recording layer, etc.

Water-soluble binders include natural high molecular weight compounds such as proteins (e.g., gelatin, albumin, casein), cellulose derivatives (e.g., carboxymethyl-cellulose, hydroxyethylcellulose), sucrose (e.g., agar-agar, sodium alginate, carboxymethylated starch, gum arabic), etc.; and synthetic water-soluble high molecular weight compounds such as poly(vinyl alcohol), polyvinylpyrrolidone, poly(acrylic acid), polyacrylamide, styrene/butadiene/methacrylic acid latex, acrylonitrile/butadiene/acrylic acid latex, styrene/maleic anhydride copolymer.

The volume average particle size of the inorganic pigment is measured in the following manner.

The inorganic pigment is dispersed with stirring into 100 ml of a 1 wt% sodium chloride aqueous solution at a concentration of 10 to 100 ppm. The resulting dispersion is subjected to a particle size distribution measuring apparatus "Coulter Counter Model TA", a product of Coulter Electronics Inc., (Healeah, Florida, USA) to measure the particle size.

There are no special limitations on the color former which reacts with the recording sheet of the instant invention to develop color; suitable compounds include the following: (1) triarylmethane derivatives; 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide (Crystal Violet lactone), 3,3-bis(p-dimethylaminophenyl)phthalide, 3-(p-dimethylaminophenyl-3-(1 ,2- dimethylindole-3-yI)phthalide, 3-(p-dimethylaminophenyl)-3-(2-methylindole-3-yI)phthalide, 3-(p- dimethylaminophenyl)-3-(2-phenylindole-3-yI)phthalide, 3,3-bis( 1 ,2-dimethylindole-3-yl)-5- dimethylaminophthalide, 3,3-bis( 1 ,2-dimethylindole-3-yl)6-dimethlaminophthalide, 3,3-bis(9- ethylcarbazole-3-yI)-5-dimethylaminophthalide, 3,3-bis(2-phenylindole-3-yl)-5- dimethylaminophthalide, 3-p-dimethylaminophenyl-3-( 1 -methyl-pyrrole-2-yl)-6 dimethylaminophthalide, (2) diphenylmethane compounds; 4,4'-bis-dimethylaminobenzhydrine benzyl ether, N-halophenylleucoauramine, N-2,4,5-trichlorophenylleucoauramine, (3) xanthene compounds;; Rhodamine B anilinolactam, Rhoda mine B p-nitroanilinolactam, Rhodamine B p-chloroanilinolactam, 7 dimethylamino-2-methoxyfluorane, 7-diethylamino-2-methoxyfluorane, 7-diethylamino-3- methoxyfluorane, 7-diethylamino-3-chlorofl uorane, 7-diethylamino-3-chloro-2-methylfluorane, 7- diethyla mino-2 ,2-di methylfluorane, -/-diethyl a mi no-3-acetyl methyla minofluorane, 7-di-ethylamino-3'- methylaminofluorane, 3,7-diethylaminofluorane, 7-diethyl-amino-3-dibenzylaminofluorane, 7- diethylamino-3-methylbenzylaminofluorane, 7-diethylamino-3-chloroethylmethylaminofluorane, 7- diethylamino-3-diethylaminofluorane, (4) thiazine compounds; benzoylleucomethylene blue, pnitrobenzoylleucomethylene blue, (5) spiro compounds; 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro- dinaphthopyran, 3,3'-dichloro-spiro-dinaphthopyran, 3-benzylospiro-dinaphthopyran, 3-methyl- naphtho-(3-methoxybenzo)-spiro-pyran, 3-propyl-spiro-dibenzopyran. They may be used individually or in combination. Such compounds are selected and used depending on the application and the performance expected.

The color former is dissolved in an oil. The resulting oil solution may be sealed in capsules or dispersed in a binder solution. Such capsules or the dispersion can be spread over a support. Oils used for the dissolution of color former include synthetic as well as natural oils and mixtures thereof.

Preferred materials are exemplified by cottonseed oil, kerosene, paraffin, naphthenic oil, alkylated biphenyl and terphenyl, alkylated naphthalene, triarylmethane, chlorinated paraffin and diarylethane.

For the preparation of capsules, reference can be made to the following patents: (1) U.S. Patents 2,800,457, 2,800,458, 3,041,289 and 3,687,865, (2) surface polymerization method; U.S. Patents 3,492,380 and 3,577,515, British Patents 950,433, 1,046,469 and 1,091,141, (3) internal polymerization method; British Patent 1,237,498, French Patents 2,060,818 and 2,090,862, (4) external polymerization method; British Patent 989,264, Japanese Patent Publication Nos.

12380/1962, 14327/1962, 29483/1970, 7313/1971, and 30282/1971.

Recording sheet materials of the present invention can be obtained by spreading coating mixtures over suitable supports such as paper, synthetic paper or plastic films, and then drying the coated products. Any coating method known in the art can be employed. Examples are air-knife coating, roll coating, blade coating, size-press coating and curtain coating. A single or multiple layers can be provided with a single coating operation.

Each of the recording layer and the color former layer of the present invention is provided on the same or different side of a common support, or on the surface of different supports. With the application of writing pressure or impact pressure, the electron-donating organic color former in the microcapsules is released to cause reaction with the metal salt of the organic acid whereby an image is recorded in response to the intensity of the pressure applied.

The coating rate of the recording layer depends on the type of the metal salt of the organic acid, the inorganic pigment used and, further, the binder. A suitable rate usually lies in the following ranges for each of the essential ingredients: for the synthetic color developer agent, about 0.2 g/m2 to about 1 g/m2, and for the inorganic pigment about 1.8 to about 10 g/m2. When the amount of the synthetic color developing agent is below 0.2 g/m2, the light fastness of the recording sheet deteriorates, while with the coating rate for the inorganic pigment below 1.8 g/m2, printing inks dry unacceptable slowly.

Further, if the coating rate for the organic pigment is above 1.8 g/m2, the initial color developability deteriorates under a low pressure when the amount of the synthetic color developing agent is below 0.2 g/m2. The upper limit for each ingredient is determined from an economical point of view rather than from performance.

The value for oil absorbance should preferably lie between about 45 and 200. Below 45, the ink setting property deteriorates. The volume average particle size should be from about 0.1 to 8 microns.

Coarser pigments with the volume average particle size of not less than 8 microns again adversely affect the ink setting performance.

As has been stated above, the recording material of the instant invention has characteristically an excellent light-fastness and an improved printing ink setting property. The advantageous features realized in the recording materials of the instant invention have been confirmed by the use of the following color former sheet.

Microcapsules containing the color former were formed according to the method set forth in, for example, U.S. Patent 2,800,457, which method will be described in detail in the following Examples in which all parts are by weight.

A color former solution was prepared by dissolving 4% Crystal Violet lactone in diisopropylnaphthalene. Into 600 ml hot water kept at 400C were dissolved under stirring 100 parts of an acid-treated gelatin having an isoelectric point of 8.2 and 100 parts of gum arabic. Further, 2 parts of turkey-red oil was added as emulsifier. To the resulting solution was added 500 parts of the color former-containing oil under vigorous stirring. When the oil droplets were emulsified to have a droplet size of 7-8 microns, the agitation was stopped. 3200 parts of 400C water was then added with stirring with care that the fluid temperature did not fall below 400 C. Next, the pH of the fluid was adjusted at 4.5 by the addition of 80 wt% aqueous acetic acid to establish a coacervation condition.

After another 20 minutes agitation, the entire volume was cooled by icy water whereby the coacervated membrane having deposited around the oil droplets gelled. When the fluid temperature went down to 200C, 70 parts of a 37 wt% aqueous formaldehyde solution was added. When the fluid temperature further dropped to 1000, 250 parts of a 10 wt% aqueous carboxymethylcellulose solution (having a degree of etherification of 0.73 and a mean molecular weight of 50,000) was added, and then the pH was adjusted to about 10 by the addition of a 1 5 wt% aqueous sodium hydroxide solution.

These operations were performed under continued agitation. Then the fluid temperature was raised to 500C with stirring. The resulting microcapsule dispersion was finally adjusted to a temperature of 300 C.

A coating mixture was prepared by adding to this dispersion 500 parts of a 10 wt% aqueous poly(vinyl alcohol) solution and 50 parts of finely-divided cellulose as cushioning agent with thorough stirring.

The coating mixture was spread over a 40 g/m2 base paper with an airknife coated to give a nonvolatile coating rate of 6.0 g/m2 and dried.

In this way, a recording sheet coated with microcapsules containing Crystal Violet lactone as dye precursor was obtained.

Example 1 120 parts of activated white clay having an oil absorbance of 64 and a volume average particle size of 6.5 microns were dispersed together with 10 parts of zinc 3,5-di-a-methylbenzylsalicylate into 200 parts of water containing 1 part of sodium hexametaphosphate by means of Kady mill. This dispersion was passed through a sandgrinder (Type 32 G available from Igarashi Machinery Co.,) at a feed rate of 3001/her. To the thus ground dispersion were added 50 parts of a 10% aqueous poly(vinyl alcohol) (PVA-1 1 7 manufactured by Kurare Co.) solution and 20 parts of a carboxylated SBR latex (solid content: 48%).

After agitation to thorough homogeneity, water was added to give a solid concentration of 20%.

A recording sheet was obtained by coating the thus prepared coating mixture so as to give a coating rate of 5.5 g/m2 as solid ingredient with an airknife coated followed by drying.

Example 2 In place of the activated white clay used in Example 1, 120 parts of kaolin (Shinshu kaolin) having an oil absorbance of 52 and a volume average particle size of 5.4 microns were used and the same procedures were repeated as those in Example 1 to prepare another recording material.

Comparative Example 1 All the procedures in Example 1 were repeated precisely except that the activated white clay was substituted with the same amount of talc having an oil absorbance of 35 and a volume average particle size of 9.2 microns.

Comparative Example 2 To prepare still another recording material, the procedures in Example 1 were repeated without zinc 3,5-a-methylbenzylsalicylate in the coating mixture.

Comparative Example 3 The procedures of Example 1 were repeated precisely only in place of the activated white clay, 120 parts of kaolin (Georgia kaolin) with an oil absorbance of 32 and a volume average particle size of 3.5 microns was employed.

Comparative Example 4 Another recording material was prepared in the same manner as in Example 1 except that the amount of zinc 3,5-di--methylbenzylsalicylate added was 4 parts instead of 10 parts. The amount of a synthetic color developer coated was 0.15 g/m2.

Test Methods (a) Light Stability of Developed Dye Image The above-described complementary sheet coated with microcapsules containing Crystal Violet lactone was superimposed on each of the recording sheet materials prepared in each Example and Comparative Example above and typewritten at a low type pressure. The developed dye image was exposed indoors at 600 lux light intensity for a week. The changes in the image density and the hue of the images were measured.

(b) Drying Speed of Printing Ink The recording sheet prepared in each of the above described Examples were subjected to roll printing with varying inking rates with a relief printing ink (SKATA ink for type printing, Sepia, tackiness of 8.2, a product of Sakata Shokai). The adhesion of the ink to be printed surface (the coated side of the sheet), and the ink offset on the opposite side of the adjacent sheet were compared at the inking rate where the printed image appeared most sharp and distinct.

(c) Initial Color Developability Under Low Pressure The above-described microcapsule sheet was superimposed on each of the recording sheet materials prepared in each Example and Comparative Example above. The developed dye image was formed under a pressure of 100 Kg/cm2 for 5 minutes. The changes in the images density after 1 5 minutes were measured.

The results of these comparisons are summarized in the following table.

Table Initial Light Stability Printing Ink color develop Image Image Setting ability under Density Hue Adhesion Setting a low pressure Example 1 high good good good good Example 2 high good good good good Comparative slightly good poor poor poor Example 1 low Comparative Example 2 low poor good good poor Comparative Example 3 high good poor poor poor Comparative Example 4 high poor good good poor In the table, "good" and "high" mean practically acceptable, while "low" and "poor" mean practically unacceptable.

The above results confirm the prominent features achieved by the present invention.

Claims (14)

Claims

1. A colour developer composition comprising a synthetic color developing agent, an inorganic pigment and a binder, said inorganic pigment having an oil absorbance as herein defined of not less than 45 and a volume average particle size of not larger than 8 microns.

2. A composition as claimed in Claim 1, wherein said inorganic pigment has an oil absorbance of from 45 to 200.

3. A composition as claimed in Claim 1 or 2, wherein said inorganic pigment has a volume average particle size of from 0.1 to 8 microns.

4. A composition as claimed in any preceding claim, wherein said binder is water soluble.

5. A composition as claimed in any preceding claim, wherein said synthetic colour developer is a metal salt of an aromatic or an aliphatic carboxylic acid.

6. A composition as claimed in Claim 5, wherein said aromatic carboxylic acid is represented by the following general formula:

wherein R1-R5 may be the same or different and each represents a hydrogen atom, a halogen atom, a hydroxyl group, an amino group, an alkylamino group, a nitro group, an aldehyde group, an alkyl group, a cycloalkyl group, an aryl group, an alkaryl group, an aralkyl group, or an alkoxy group, or R, and R2 or R3 and R4 may together to form a 5- or 6-membered ring.

7. A composition as claimed in Claim 5, wherein said aliphatic acid is a C4-C26 saturated monobasic or polybasic aliphatic acid or a C10-C24 unsaturated monobasic or polybasic aliphatic acid.

8. A composition as claimed in any one of Claims 5 to 7, wherein said aliphatic or aromatic carboxylic acid salt is a salt of a metal selected from Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, K, Ge, Sr, Y, Zr, Mo, Ag, Cd, In, Sn, Sb, Ba, W, Pb, Bi and Na.

9. A composition as claimed in Claim 1 and substantially as herein described.

10. A colour developer composition substantially as herein described with reference to Example 1 or2.

11. A colour developer sheet comprising a sheet support having one surface thereof coated with a composition as claimed in any preceding claim, said agent being coated in an amount of not less than 0.2 g/m2 and said pigment being coated in an amount of not less than 1.8 g/m2.

12. A sheet as claimed in Claim 11, wherein said agent is coated in an amount of from 0.2 to 1 9lem2.

1 3. A sheet as claimed in Claim 11 or 1 2, wherein said pigment is coated in an amount of from 1.8 to 10g/m2.

14. The features as herein disclosed, or their equivalents, in any novel selection.

14. Recording material comprising a sheet as claimed in any one of Claims 11 to 13 and, coated on said one surface or on the opposite surface of said support, or on a surface of a different support, a layer containing a colour former.