NO139432B - SHEET FOR USE IN A PRESSURE SENSITIVE COPYING SYSTEM - Google Patents

Description

The present invention relates to a sensitized sheet which can be used in a pressure-sensitive copying system. more especially one. sensitized sheet which has a coating consisting of an acceptor which

Is able to form a color when it comes into contact with a colourless, chromogenic compound.

The pressure-sensitive copying system according to the present invention generally uses a color-forming reaction between a electron-donating colorless compound'and .an electron-accepting solid acid.

Different types of pressure-sensitive copying sheets are known. US Patent No. 2,730,456 thus describes pressure-sensitive copying sheets of the overlay type where an upper or overlying sheet is coated with a layer. containing microcapsules in which it is placed, an "electron-releasing colourless" compound-.

(hereinafter referred to as "the color former") dissolve in an oil-like solvent, as well as an underlying sheet sensitized with a note,. •-containing an electron-accepting or accepting .-solid acid '-(hereinafter referred to as "the acceptor") ... The color former is transferred' to

the underlying sheet when the microcapsule is broken into pieces, and a visible colored image is formed on the next underlying sheet. If more copies are desired, an intermediate sheet with

microcapsules on one side and the acceptor on the other. between the top and bottom sheets.

Said patent describes, too. a copying sheet where both the fine capsules and the acceptor are coated on the same side, a so-called "seif contained" copying sheet.

German Patent No. 1,275-550 further describes a print-sensitive copying sheet in which the copy-forming compounds which are soluble in a liquid solvent are carried on the surface 6 g7e.il is the inside of a carrier layer, and in which said solvent is present isolated from at least one of said colour-forming components, by means of pressure-degradable capsules.

Examples of the color former include the "Leuco" type

of chromogenic compounds - such as crystal violet lactone, benzoyl-leucomethylene blue, malachite green lactone, . rhodamine-B-lactone,

fluorane derivatives and spiropyrans. Known acceptors include acid clay, activated clay,

. attapulgite, kaolin and other inorganic solid acids, but they have the disadvantage that the developing color image is bleached by exposure to moisture and sunlight. A pressure-sensitive sheet coated with an organic solid acid such as "phenolic resins" has also been used. Such sheets, however, tend to turn yellow under the influence of sunlight, and the developed color image has a decreasing density or disappears little by little due to heat or humidity. As other examples of the organic solid acid, •can be mentioned aromatic carboxylic acids (US Patent Nos. 3,322,557 and 3,488,207) and polyvalent metal salts of aromatic carboxylic acids (DT-OS 2,152,765). It is, for example, described benzoic acid,, o-nitrobenzoic acid, o-chlorobenzoic acid, 4-methyl-3-nitrobenzoic acid, p-isopropylbenzoic acid, p-tert-butylbenzoic acid,. salicylic acid, 5-tert-butylsalicylic acid, 3-cyclohexylsalicylic acid, 3-methyl-5-isoamyl-salicylic acid, 3.,5-dinitrosalicylic acid, 1-naphthaoic acid, 1-hydroxy-2-naphthoic acid,' 5, 5 '-methylenedisalicylic acid and other similar ■ aromatic ..carboxylic acids, -as well as salts of. metals such as magnesium, calcium, zinc, cadmium, aluminium, gallium, tin, lead, chromium, molybdenum, manganese, cobalt and nickel together with the above-mentioned vessels. carboxylic acids'.. Such, aromatic carboxylic acids. and polyvalent metals are superior in terms of stability to the influence of sunlight compared to said phenolic resins. However, some of the mentioned aromatic carboxylic acids and polyvalent metal salts have a certain sublimation ability, and a sheet sensitized with a coating containing such acceptors therefore loses its color-forming ability over time. As said acceptors are relatively soluble in water and thus diffuse into the sheet itself, under the influence of high humidity or water, the color forming ability on the surface of the sheet is lost. These disadvantages' increase

significantly as one lowers the molecular weight of.the aromatic carboxylic acid.. The reason for. that salicylic acid was previously proposed,

but not used in practice, is that it has the aforementioned disadvantage as well as weak color density. Some aromatic carboxylic acids and polyvalent metal salts show improved resistance to heat and moisture as the molecular weight increases, and they can maintain relatively

stable color-forming properties at normal temperature and humidity. There are, however, considerable opportunities to improve the properties required in practice of pressure-sensitive copy paper. It is inevitable that copy paper is stored or processed under conditions which entail high moisture or direct water contact with the sheet. It often happens, for example, that rainwater or water droplets stick to the sheet. In certain cases, it happens that when a letter or figure is printed using offset on the upper or lower side of a pressure-sensitive copying sheet, then a solution will be transferred from the offset machine to an acceptor-coated surface of the sheet. - If, under such circumstances, the organic acid has insufficient resistance to high humidity or water, -will one obtains a copying sheet with markedly reduced color-forming ability.. 1 those cases-where the sensitized sheet-is in contact

with one other'sheet of - the encapsulated colorant.n, "so- will. it

-.organic acids come into contact with color formation "with the help of" the moisture .or water as.a carrier, whereby "one gets an unwanted color formation which..is often called "staining". '

A layer containing, the acceptor. now therefore have .hoy resi-': stens -against moisture or water, "so that one can maintain '.. '. a stable color-forming ability due to a developed color image, in addition to preventing "spotting". dis see, must on account ; ' ,.•-'':. of its instability to heat, on the other hand, must be controlled and handled during storage or coating". Especially during the coating, the composition will be subjected to mechanical shear forces which are often followed by rising temperature. If you therefore have insufficient mechanical stability and thermal stability, so'

will the_coating composition not form a uniform: layer on" the surface of a base sheet, and in the worst cases the actual work must be interrupted". If the coating is carried out by a coating device placed on a paper machine, this is the simplest process and therefore very advantageous economically. As the coating in this case is coated on a base sheet which is preheated by means of a

drier, this increases the demand for thermal stability and mechanical stability. . It is therefore an aim of the present invention to provide a sensitized sheet for a pressure-sensitive copier. ing system. which has excellent resistance to heat, light and especially..h6y humidity or water, and which is -isand' to' maintain a stable, f color-forming. ability .. The above-mentioned 'objectives and advantages' are achieved according to the present invention by a sheet for use in a printing press like. copying system, sensitized with a coating for producing color on contact with a chromogenic material, which coating contains at least one acidic compound selected from among aromatic carboxylic acids and polyvalent metal salts thereof, and the sheets according to the invention are characterized by the fact that the coating contains a homogeneous mixture in particulate form of: '(a) ' . , 100 parts acidic compound, and (b) 5-300 parts by weight of at least one solid compound with a molecular weight above 400, selected from polystyrene, styrene copolymers, α-methylstyrene polymers, α-methylstyrene copolymers,'. polyvinyl chloride, vinyl chloride copolymers, yinylidene chloride copolymers,. polychloroprene, cyclopentadiene polymers, cyclopentadiene copolymers, acrylic ester polymers, acrylic ester copolymers, acrylic acid copolymers, methacrylic ester polymers, methacrylic ester copolymers. methacrylic acid copolymers, vinyl acetate polymers, vinyl acetate copolymers, such as ethylene vinyl acetate copolymers, acrylonitrile copolymers, acrylamide copolymers; allyl alcohol copolymers benzyl chloride polycondensation products, benzyl chloride polycondensation products, metaxylene formaldehyde condensates, diphenyl formaldehyde cocondensates and diphenyl metha xylene formaldehyde condensation products.

The mixture of the organic acid compound and the organic high molecular compound in it can be pulverized into a uniform fine powder, the particle size of which is a few microns, mechanically, e.g. by grinding in a ball mold. In this way, a coating is obtained where the fine powder is homogeneously dispersed, whereby very distinct images are obtained.

The organic acid compound to be used in the present invention is selected from the group consisting of aromatic carboxylic acids and polyvalent metal salts thereof. Such connectors are illustrated below by way of example, and it--'

it is of course understood that other aromatic carboxylic acids "and polyvalent metal salts thereof can also be used, as long as the said compounds are able to produce a color when brought into contact with a color former.

An aromatic carboxylic acid that can be used can be represented by formula I.

where R^, R2j R^j R^ and R^ each represent hydrogen, halogen or groups such as hydroxyl, amino, carboxyl, carbamyl, N-substituted carbamyl, alkyl, cycloalkyl, alkoxy, aryl, aryloxy, aralkyl or alkylaryl, and any adjacent pair of R^ to' can together with the carbon atoms to which they are attached,-...form . a -. call, e.g. 'a petroleum ring. Compounds of formula I where R 1 or R 1 - is a hydroxyl group are particularly important in certain embodiments of the present invention.

Examples of aromatic carboxylic acids of the formula wherein and R^ is not a hydroxyl group include benzoic acid, o-toluic acid, m-toluene acid, p-toluene acid, p-tert-butylbenzoic acid, o-chlorobenzoic acid, m-chlorobenzoic acid, p-chlorobenzoic acid, < d>iclorbenzor-.

acid, trichlorobenzoic acid, tetrachlorobenzoic acid,. phthalic acid, isbphthalic acid, terephthalic acid, 2-carboxybiphenol, p-oxybenzoic acid, para-, methoxybenzoic acid, p-butoxybenzoic acid, p-octbxybenzoic acid, gallusr acid, anthranilic acid, phthalic acid monoamide, phthalic acid mqnoanilide, 3-tert. butyl-4-hydroxybenzoic acid, 3-cyclohexyl-4-hydroxybenzoic acid,

3-phenyl-4-hydroxybenzoic acid, 3-(a-methylbenzyl)-4-hydroxybenzoic acid, 3,5-dimethyl-4-hydroxybenzoic acid, trimellitic acid, pyromellitic acid, a-naphthoic acid, |3-naphthoic acid, tetrachlorophthalic acid and 2,Z^dicarboxydiphenyl.

Aromatic carboxylic acids of formula I where R-j_- or R^ is a hydroxyl group are defined by formula II where Rg to Rg are as defined for R-^ to R^ in formula I.

Examples of such carboxylic acids include salicylic acid', o-cresotic acid, p-cresotic acid, 3-ethylsalicylic acid, 4-ethylsalicylic acid, 3-isopropylsalicylic acid, 4-isopropylsalicylic acid, 5-isopropylsalicylic acid, 3-tert-butylsalicylic acid, 5-tert-butylsalicylic acid -acid, 3-cyclohexylsalicylic acid, 5-cyclohexylsalicylic acid, 3-phenylsalicylic acid, 5-phenylsalicylic acid, 3-benzylsalicylic acid, 5-tert-octylsalicylic acid, 3-(oc-methylbenzyl)-salicylic acid, 5-(cc-methylbenzyl)-salicylic acid, 5 -nonylsalicylic acid, 5-(α,α-dimethylbenzyl)-salicylic acid, 5-chlorosalicylic acid, 5-butoxysalicylic acid and 5-octoxy-salicylic acid.

Compounds of formula II where Rg and RQ are halogen, alkyl, cycloalkyl, aryl, aralkyl or alkylaryl can easily be prepared on a commercial scale from phenols, alkylphenols, arylphenols or halogenated phenols. Examples of such aromatic carboxylic acids include 3,5-dichlorosalicylic acid, 3-chloro-5-tert-butylsalicylic acid, 3-chloro-5-tert-amylsalicylic acid, 3-chloro-5-tert-octylsalicylic acid, 3-chloro-5- (α,α-dimethylbenzyl)-salicylic acid, 3»5-dimethylsalicylic acid, 3-methyl-5-tert.-butylsalicylic acid, 3-methyl-5-cyclohexylsalicylic acid, 3-methyl-5-tert.-octylsalicylic acid, 3-methyl- 5-(a-methyl-benzyl)-salicylic acid, 3-methyl-5-nonylsalicylic acid, 3-methyl-5-(a,a-dimethylbenzyl)-salicylic acid, 3,5-diisopropylsalicylic acid, 3,5-di-sec. -butylsalicylic acid, 3-tert-butyl-5-chlorosalicylic acid, 3-tert-butyl-5-methylsalicylic acid, 3-tert-butyl-5-ethylsalicylic acid, 3,5-di-tert-butylsalicylic acid, 3-tert .-butyl-5-cyclohexylsalicylic acid, 3-tert.-butyl-5-phenylsalicylic acid, 3-tert.-butyl-5_(4<1->tert.-butylphenyl)-salicylic acid, 3-tert.-amyl-5- chlorsalicylic acid, 3-tert.-amyl-5-methylsalicylic acid, 3-tert-amyl-5-ethylsalicylic acid, 3,5-di-tert.-amylsalicylic acid, 3-tert.-amyl-5-cyclohexylsalicylic acid, 3-tert.- amyl-5-phenylsalicylic acid, 3-tert.-amyl-5-(4' - tert.-amy lphenyl)-salicylic acid, 3-cyclohexyl-5-chlorosalicylic acid, 3-cyclohexyl-5-methylsalicylic acid, 3-cyclohexyl-5-ethylsalicylic acid, 3,5-dicyclohexylsalicylic acid, 3-cyclohexyl-5-phenylsalicylic acid, 3-cyclohexyl-5-( 4'-cyclohexylphenyl)-salicylic acid, 3-phenyl-5-chloro-.salicylic acid, 3-phenyl-5-isopropylsalicylic acid, 3-phenyl-5-tert.-butylsalicylic acid, 3-phenyl-5-tert.-amylsalicylic acid, 3 -phenyl-5-cyclohexylsalicylic acid, 3-phenyl-5-benzylsalicylic acid, 3-phenyl-5-ter.t.-octylsalicylic acid, 3-phenyl-5-(a-methylbenzyl)-salicylic acid, 3-phenyl-5-nonylsalicylic acid, 3-phenyl-5-(α,α-dimethylbenzyl)-salicylic acid, 3-benzyl-5-chlorosalicylic acid, 3-benzyl-5-methylsalicylic acid, 3-benzyl-5-ethylsalicylic acid, 3-benzyl-5-cyclohexylsalicylic acid, 3- benzyl-5-phenylsalicylic acid, 3,5-dibenzylsalicylic acid, 3-benzyl-5-tert.-pctylsalicylic acid, 3-benzyl-5-nonylsalicylic acid, 3-benzyl-5-(a,a-dimethylbenzyl)salicylic acid, 3-tert. -octyl-5-chlorosalicylic acid, 3-tert-octyl-5-methylsalicylic acid, 3-tert-octyl-5-ethylsalicylic acid, 3-tert-octyl-5-cyclohexylsalicylic acid, 3-tert .-octyl-5-phenylsalicylic acid, 3,5-di-tert.-octylsalicylic acid, 3-(a-methylbenzyl)-5-chlorosalicylic acid, 3-(a-methylbenzyl)-5-methylsalicylic acid, 3-(a- methylbenzyl)-5-ethylsalicylic acid, 3-(cc-methylbenzyl)-5-cyclohexylsalicylic acid, 3-(q-methylbenzyl)-5-phenylsalicylic acid, 3,5-di(a-methylbenzyl)salicylic acid, 3-(oc-methylbenzyl) -5-(a,a-dimethylbenzyl)-salicylic acid, 3-(a-methylbenzyl)-5-/4*'-(a-methylbenzyl)-phenyl7-salicylic acid, 3-nonyl-5-chlorosalicylic acid, 3- nonyl-5-methyl-salicylic acid, 3-nonyl-5-ethylsalicylic acid, 3-nonyl-5-phenylsalicylic acid, 3,5-dinonylsalicylic acid, 3-(a,a-dimethylbenzyl)-5-chlorosalicylic acid,

3-(a,a-dimethylbenzyl)-5-methylsalicylic acid, 3-(a,a-dimethylbenzyl)-5-t.-amylsalicylic acid, 3-(a,a-dimethylbenzyl)-5-ethylsalicylic acid., 3-(a ,α-dimethylbenzyl)-5-cyclohexylsalicylic acid, 3-(α,α-dimethyl-benzyl)-5-phenylsalicylic acid, 3-(α,α-dimethylbenzyl)-5-(α-methylbenzyl)-salicylic acid, 3,5 -di(α,α-dimethylbenzyl)-salicylic acid, 3-(4'-tert-butylphenyl)-5-tert-butylsalicylic acid, 3-(4'-cyclohexyl-phenyl)-5-cyclohexylsalicylic acid and 3-^4 '-(α,α-dimethylbenzyl)-phenyl7-5-(α,α-dimethylbenzyl)-salicylic acid.

Aromatic carboxylic acids of formula II where R 1 or R 2 is alkyl, cycloalkyl or phenyl, can e.g. are prepared from metacresol, metapropylphenol, metaphenylphenol, 2,3-xylenol, 2,5-: xylenol, 3>4-xylenol and 3,5-xylenol. Examples of such carboxylic acids include 3,4-dimethylsalicylic acid, 4,5-dimethylsalicylic acid , 4,6-dimethylsalicylic acid, 4-methyl-5-isopropylsalicylic acid, 4-methyl-5-sec.-butylsalicylic acid, 4-methyl-5-tert.-butylsalicylic acid, 4-methyl-5-tert.-amylsalicylic acid, 4-methyl-5-cyclohexylsalicylic acid, 4-methyl-5-benzylsalicylic acid, 4-methyl-5-tert-octyl-salicylic acid, 4-methyl-5-(a-methylbenzyl)-salicylic acid, 4-methyl-5-nonylsalicylic acid , 4-methyl-5-(a,a-dimethylbenzyl)-salicylic acid, 3,6-dimethylsalicylic acid , 3-tert.-butyl-6-methylsalicylic acid, 3-tert.-amyl-6-methylsalicylic acid, 3-cyclohexyl-6 -methylsalicylic acid, 3-tert.-octyl-6-methylsalicylic acid, 3-(a-methylbenzyl)-6-methyl-salicylic acid, 3,6-diisopropylsalicylic acid, 3-tert.-butyl-6-isopropylsalicylic acid, 3-tert.- Octyl-6-isopropylsalicylic acid, 3-(a,a-dimethylbenzyl)-6-isopropylsalicylic acid, 3-tert-butyl-6-phenylsalicylic acid, 3-tert-amyl-6-phenylsalicylic acid, 3-cyclic ohexyl-6-phenylsalicylic acid, 3-tert-octyl-6-phenylsalicylic acid, 3-(α-methylbenzyl)-6-phenylsalicylic acid or 3-(α,α-dimethylbenzyl)-6-phenylsalicylic acid.

Aromatic carboxylic acids of formula II where at least

one of the groups Rg to Rg is a hydroxyl group, can be indicated by formula III

where m is 1 or 2, or a number from 0 to 3, R is an alkyl-cycloalkyl- or aralkyl group. Examples of such carboxylic acids include 3-hydroxysalicylic acid, 3-hydroxy-5-tert-butylsalicylic acid, 3-hydroxy-5-tert-amylsalicylic acid, 3-hydroxy-5-cyclohexylsalicylic acid, 3-hydroxy-5-tert- octylsalicylic acid, 3-hydroxy-Sy_5_(a-methylbenzyl)-salicylic acid, 3-hydroxy-5-(a,a-dimethylbenzyl) salicylic acid, 3-hydroxy-4,6-dlcyclohexylsalicylic acid, 4-hydroxysalicylic acid, 4-hydroxy-5- tert-butylsalicylic acid, 4-hydroxy-5-tert-amylsalicylic acid, 4-hydroxy-5-cyclohexylsalicylic acid, 4-hydroxy-5-tert-octylsalicylic acid, 4-hydroxy-5-(a-methylbenzyl)-salicylic acid, 4 -hydroxy-5-(α,α-dimethylbenzyl)salicylic acid, 3,5-diisopropyl-6-hydroxysalicylic acid, 3,5-di-tert.-butyl-6-hydroxysalicylic acid, 3,5-di-tert.- amyl-6-hydroxysalicylic acid, 3,5-di-cyclohexyl-6-hydroxysalicylic acid, 3,5-di(a-methylbenzyl)-6-hydroxy-

sysalicylic acid, 3,5-di(a,a-dimethylbenzyl)-6-hydroxysalicylic acid, 5-hydroxysalicylic acid, 4-tert-butyl-5-hydroxysalicylic acid, 4-tert-amyl-5-hydroxysalicylic acid, 4-cyclohexyl-5 -hydroxysalicylic acid, 4-(α-methylbenzyl)-5-hydroxysalicylic acid, 3,6-diisopropyl-5-hydroxysalicylic acid, 3,6-dicyclohexyl-5-hydroxysalicylic acid or 3,6-di(α-methylbenzyl)- 5-hydroxysalicylic acid.

In those cases where adjacent pairs of the groups Rg to Rg form a ring together with the carbon atoms to which they are bound, naphthalene derivatives are formed. These can be indicated by the formulas IV, V and VI,

where R^, R'2, R'5, R'^, R<1>^, R'g, R'7 and R<»>8 are each hydrogen, halogen or a hydroxyl-, alkyl-, cycloalkyl- or aralkyl group. Examples of such naphthalene derivatives include 1-hydroxy-2-carboxynaphthalene, 1-hydroxy-2-carboxy-4-isopropylnaphthalene, 1-hydroxy-2-carboxy-4-cyclohexylnaphthalene, 1-hydroxy-2-carboxy-4-benzylnaphthalene , 1-hydroxy-2-carboxy-4-(α-methyl-

benzyl)-naphthalene, 1-hydroxy-2-carboxy-7-isopropylnaphthalene, 1-hydroxy-2-carboxy-7-tert.-butylnaphthalene, 1-hydroxy-2-carboxy-7-tert.-amylnaphthalene, 1 -hydroxy-2-carboxy-7-cyclonaphthalene, 1-hydroxy-2-carboxy-7-tert,-octylnaphthalene, 1-hydroxy-2-carboxy-7-(a-methylbenzyl)-naphthalene, 1-hydroxy- 2-carboxy-7-(α,α-dimethylbenzyl)-naphthalene, 1-hydroxy-2-carboxy-4,7-diiso-propylnaphthalene, 1-hydroxy-2-carboxy-4,7-di-tert-butylnaphtha -lene, 1-hydroxy-2-carboxy-4,7-di-tert-amylnaphthalene, 1-hydroxy-2-carboxy-4,7-dicyclohexylnaphthalene, 1-hydroxy-2-carboxy-4,7-dibenzylnaphthalene, 1-hydroxy-2-carboxy-4,7-di-tert-octylnaphthalene, 1-hydroxy-2-carboxy-4,7-di(α-methylbenzyl)-naphthalene, 1-hydroxy-2-carboxy -4,7-di(a,a-dimethylbenzyl)naphthalene,.1-carboxy-2-hydroxynaphthalene, 1-carboxy-2-hydroxy-3,6,8-tri-tert-butylnaphthalene, 2-hydroxy -3-carboxynaphthalene, 2-hydroxy-3-carboxy-6,8-di-tert.-butylnaphthalene, 2-hydroxy-3-carboxy-6,8-di-tert.-amylnaphthalene, 2-hydroxy-3 -carboxy-6,8-dicyclohex sylnaphthalene, 2-hydroxy-3-carboxy-6,8-di-tert.-octylnaphthalene, 2-hydroxy-3-carboxy-6,8-di(a-methylbenzyl)-naphthalene and 2-hydroxy- 3-Carboxy-6,8-di(α,α-dimethylbenzyl)-naphthalene.

Aromatic carboxylic acids derived from e.g. from bisphenol A, 4,4'-dihydroxycyclohexylidenebiphenyl, 4,4'-dihydroxymethylenebiphenyl, and 2,2'-dihydroxydiphenyloxide are believed to be condensates of salicylic acid. Examples of such carboxylic acids include 5,(4'-hydroxybenzyl)-salicylic acid, 5-(3'-carboxy-4'-hydroxy-benzyl)-salicylic acid-(methylene-bis-salicylic acid), 3-tert-butyl-5 -(3',5,-di-tert-butyl-4-hydroxybenzyl)-salicylic acid, 3-(a,a-dimethylbenzyl)-5-/3',5<1->di(a,a-dimethylbenzyl )-4'-hydroxybenzyl7-salicylic acid, 3-tert. -butyl-5-(a,a-dimethyl-3',5'-di-tert. ■-butyl-4<*->hydroxybenzyl)-salicylic acid, 5-(a,a-dimethyl-3'- carboxy-4'-hydroxybenzyl)-salicylic acid, 5-(a,a-dimethyl-4'-hydroxybenzyl)-salicylic acid, 3-(2'-hydroxyphenoxy)-salicylic acid, 3-(2'-hydroxy-3'-carboxyphenoxy )salicylic acid, 3-(2'-hydroxy-3'-carboxy-5<1->tert-butylphenoxy)-5-tert-butylsalicylic acid, 3-(2'-hydroxy-3*,5'-di- tert-butylphenoxy)-5-tert-butylsalicylic acid, 3-/2'-hydroxy-3<1->carboxy-5<1->(a,a-dimethylbenzyl)phenoxy/-5-(a,a— dimethylbenzyl)-salicylic acid, 3-/2'-hydroxy-3',5<1->di(a,a-dimethyl-benzyl)phenoxy7-5-(a,a-dimethylbenzyl)-salicylic acid and 3- (2'-hydroxy-3',5'-dicyclohexylphenoxy)-5-cyclohexylsalicylic acid.

Furthermore, a number of aromatic carboxylic acids with formula II can be mentioned which are difficult to express in ordinary chemical nomenclature. Thus, one can use co-polycondensation products of formaldehyde and salicylic acid or core-substituted salicylic acids and phenols, salicylic acid or core-substituted salicylic acid adducts of propylene polymer or is<p>butylene polymer, salicylic acid or core-substituted salicylic acid adducts of benzyl chloride polycondensation products, salicylic acid or core-substituted salicylic acid adducts of styrene polymers, salicylic acid or core-substituted salicylic acid adducts of oc -methylstyrene polymers, salicylic acid or core-substituted salicylic acid condensates of aldehydes or acetylene, salicylic acid or core-substituted salicylic acid condensates of ketones, besides salicylic acid or core-substituted salicylic acid adducts of compounds with an unsaturated bond.

The term "aromatic carboxylic acids" and "polyvalent metal salts thereof" also includes condensates and polymers as mentioned above as well as polyvalent metal salts thereof.

All of the above mentioned aromatic carboxylic acids can

form salts with polyvalent metals.

Polyvalent metals that can be used as acceptors in the present invention represent all salt-forming metals other than lithium, sodium, potassium, rubidium, cesium and francium. Thus, useful polyvalent metals include magnesium, aluminum, calcium, scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium, germanium, strontium, yttrium, zirconium, niobium, molybdenum, solv, cadmium, indium , tin, antimony, barium, tungsten, mercury, lead and bismuth. The most suitable metals in practical use are magnesium, aluminium, calcium, titanium, manganese, zinc and tin.

Of the above-mentioned aromatic carboxylic acids and polyvalent metal salts thereof, it is preferred to use compounds with at least one hydroxyl group in the benzene ring, especially a hydroxyl group in the ortho position in relation to the carboxyl group, because such compounds show the best color-forming ability. Taking into account resistance to moisture and heat as well as compatibility with high molecular organic compounds, it is preferred to use an aromatic carboxylic acid and a polyvalent metal thereof with a high molecular weight, i.e. a compound with 10 or more, preferably 17 or more carbon atoms in total. Compounds of formula II, III, IV, V and VI where the 3-position in relation to the carboxyl group is substituted with an isopropyl, secondary butyl, tertiary butyl, tert.-amyl, cyclohexyl, phenyl, substituted phenyl, benzyl, α-methylbenzyl, α,α-dimethylbenzyl, tert.-octyl, nonyl or another group with 3 or more carbon atoms, show particularly good color-forming properties, in this case stability towards water in addition to compatibility with an organic high molecular weight compound. Compounds of formula II, III, IV, V and VI which have at least one 5- or 6-carbon ring as a substituent and which have a total of more than 17 carbon atoms in the molecule are most preferred.

The polyvalent metal salts of aromatic carboxylic acids can be prepared by reacting said acids with oxides, hydroxides, carbonates or silicates of polyvalent metals, although they can conveniently be obtained by a double decomposition of an alkali metal salt of an aromatic carboxylic acid and a water-soluble polyvalent metal salt. In such cases, the aromatic carboxylic acid and the water-soluble polyvalent metal salt can each be used either alone or in a mixture of two or more. The polyvalent metal salts of said carboxylic acids are usually obtained in the form of crystalline powders, amorphous fine powders or viscous liquids.

An organic high molecular weight compound to be used

in the present invention should have a slight non-fluidizing property at normal temperature, and should preferably be selected from a group with a molecular weight of 400 or more. The following are examples of useful organic high molecular weight compounds: polybutadiene, butadiene copolymers such as butadiene isoprene copolymers such as butadiene styrene copolymers, cyclopentadiene polymers, cyclopentadiene copolymers, polystyrenes, styrene copolymers, α-methylstyrene polymers, α-methylstyrene copolymers, polyvinyl chloride, vinyl chloride copolymers, vinylidene chloride copolymers, polychloroprene (" Neoprene"), acrylic acid ester polymers, acrylic acid ester copolymers, acrylic acid copolymers, methacrylic acid ester polymers, methacrylic acid ester copolymers, methacrylic acid copolymers, vinyl acetate polymers, vinyl acetate copolymers such as ethylene-vinyl acetate copolymers, acrylonitrile copolymers, acrylamide copolymers, allyl alcohol copolymers, benzyl chloride polycondensation

products, benzyl chloride copolycondensation products, metaxylene-formaldehyde condensates, diphenylformaldehyde condensates, diphenyl-methaxylene formaldehyde copolycondensation products. It is particularly preferred to use styrene polymers, styrene copolymers, α-methylstyrene polymers and α-methylstyrene copolymers. These high-molecular compounds have good compatibility with various types of organic acid compounds and can be easily pulverized into fine powders and have a very good color-forming property.

It is highly desirable that the above-mentioned organic high molecular compound be selected from compounds having good compatibility with the organic acid compound to be mixed with it. The term "compatibility" is understood to mean such a property that two or more chemical compounds can dissolve in each other and also the case where the dissolution occurs by one crystalline substance dissolving in another.

In many cases, the compatibility of a chemical compound can be explained in terms of its polarity. In the present invention, a suitable combination of an organic acid compound and a high molecular compound will be determined based on consideration of this point. Generally, one can say that the polarity of a chemical compound can be understood qualitatively from a balance of the compound's organic and inorganic properties. An aromatic carboxylic acid usually increases its organic character and decreases its polarity as the number of carbon atoms increases. In cases where you have aromatic carboxylic acids with the same number of carbon atoms, polar radicals such as hydroxyl, carboxyl, nitro, cyano and halogen will increase the polarity if these are introduced into the molecule. The polarity will also vary depending on the type of radical and the position of the radicals in the molecule. Types of polyvalent metals that have an effect on compatibility can be expressed in terms of polarity. Thus, it can be mentioned that many polyvalent metals which tend to form polyvalent metal salts have strong inorganic properties or high polarity and are metals with a relatively small atomic weight, such as magnesium, aluminium, calcium and titanium. In contrast, zinc and tin will tend to form polyvalent metal salts with weak inorganic properties or low polarity. When, on the other hand, it concerns organic high molecular compounds, e.g. polyethylene and polypropylene,

which is considered to have the lowest polarity, will, if such groups

are introduced into double bonds, or, if they are substituted with halogen, benzene or hydroxyl, carboxyl, ether, ester, ketone, nitro, cyano or amide radicals, the polarity depends on the type and number of substituents.

As compounds of similar polarity are compatible with each other or miscible with each other, a powdered and homogeneous mixture consisting of an organic acid compound and an organic high molecular compound is obtained by choosing said high molecular compound of corresponding polarity as found in the aromatic carboxylic acid and the polyvalent metal salt.

An organic high molecular weight compound that is compatible with an organic acid compound of relatively high polarity must be selected from one of high polarity that carries polar radicals in the molecule. If, however, radicals such as -C=N, -CO-, -N=, -SO2-, -SO-, -S-, -P0=, -P=, -CS- and -O- are present in greater numbers in the molecule, they will prevent the colour-forming reaction with the colour-former, and it is therefore desirable to limit the presence of such radicals to an irreducible minimum. Halogens and a phenyl radical show no hindrance to the color reaction. In particular, it can be mentioned that hydroxyl and carboxyl radicals do not prevent the color reaction and raise the polarity even with a small number of radicals.

Although the ratio between the organic high-molecular compound and the organic acid compound is not particularly limited, in cases where the amount of the first-mentioned compound is too small, the desired resistance to heat, light and especially resistance to high humidity or water will not be achieved. It is therefore desirable to add the organic high molecular compound in amounts of 5 parts by weight (dry weight) or more, preferably from 15 - 300 parts by weight based on 100 parts by dry weight of the organic acid compound.

There are many methods for preparing a powdered mixture consisting of the organic acid compound and the organic high molecular compound. The most simple and preferred method involves the steps of mixing and melting the organic high molecular weight compound and the organic acid compound under heating, solidifying the resulting mixture on cooling and then pulverizing it. Another method involves dissolving the organic acid and the high molecular weight compound in an organic solvent, after which the resulting solution is evaporated to dryness and the residue is pulverized. The pulverization can be carried out in a tbrr system or in a wet system with a medium such as water. In certain cases, surface-active agents and fine powders with high hardness such as silicic acid anhydride and kaolin can be added to increase the actual pulverizing effect.

In the above-mentioned methods, it is preferred to use as the organic high-molecular compound one with a relatively fast glass transition point (transformation point of another order) and a relatively low molecular weight. It is usually the case that an organic high-molecular compound with a large number of ring structures in the molecule has a high second-order conversion point. In this connection, you can e.g. use polystyrene, styrene-α-methylstyrene copolymers, α-methylstyrene polymers, cyclopentadiene copolymers, aliphatic unsaturated cyclic hydrocarbon polymers, 'benzyl chloride-diphenyl polycondensation products, metaxylene formaldehyde polycondensation products, metaxylenediphenylformaldehyde copolycondensation products, metaxylene diphenyloxide formaldehyde copolycondensation products, diphenylformaldehyde polycondensation products, methacrylic acid ester polymers, acrylonitrile styrene copolymers, with molecular weights from 600 to 5000.

Alternatively, a particulate mixture can be obtained

in water-dispersed form by melting the organic acid compound and the high-molecular compound by heating or by adding an organic solvent, after which the resulting solution is dispersed in water, cooled, and if necessary, the organic solvent is removed.

Alternatively, the organic acid can be further mixed

and an initiator or regulator for a polymerization with a vinyl monomer capable of dissolving the organic acid, such as styrene, α-methylstyrene, ethyl acrylate and methyl methacrylate, after which a suspension or emulsion polymerization is produced in water, so that a particulate mixture consisting of the organic acid and an organic high molecular weight compound.

Furthermore, to produce the particulate mixture, an alkali metal or ammonium salt of an aromatic carboxylic acid can be added to an emulsion of an organic high molecular weight compound, e.g. polystyrene emulsion or styrene-butadiene copolymer emulsion, after which an acid or an aqueous solution of polyvalent metal salts is added and an acid decomposition or double decomposition is produced. In this case, heating can be used to promote a diffusion of the aromatic carboxylic acid or a polyvalent metal salt thereof into the particles of the emulsified organic high molecular compound. In this way, a finely powdered mixture is obtained in the form of an emulsion or dispersion in water.

In many cases, it will be found that the organic acid and the organic high molecular compound completely dissolve in each other into a homogeneous phase, and even if some non-dissolving parts are present in a homogeneous phase, this does not prevent the purpose of the present invention . The powder that is obtained is regulated to a particle size of normally less than a couple of microns, preferably around 0.5 microns.

In some cases, by producing a particulate mixture consisting of an organic homomole-

chylar compound, in the mixture incorporate at least one water-insoluble inorganic compound, in the form of particles, such as oxides, hydroxides and carbonates of a metal, as well as mineral pigments, in addition to an organic material in the form of a powder, such as powdered starch, powdered cellulose, and organic pigments . When you e.g. incorporates the organic acid into the organic high-molecular compound during heating, one can simultaneously add a water-insoluble inorganic material in the form of particles, e.g. such as clay, kaolin, activated clay, zinc oxide, calcium carbonate and aluminum oxide, after which the mixture is dried by cooling and finally pulverized. In this way, a particulate substrate is obtained where the mixture of the organic acid and the organic high-molecular compound is absorbed around inorganic powder particles. A further incorporation of inorganic or organic powders produces a diluting effect for the particulate substrate and improves the fluidity of the composition. An addition of inorganic powders, as mentioned below, improves the colour-forming property of the organic acid, in addition to the sensitized sheet having improved resistance to sunlight. The amount of organic matter added

. or inorganic powders are not limited as long as the organic

acid compound The ice does not stop working. It is usually preferred to use inorganic and/or organic powders in amounts of less than 2000 parts by dry weight based on 100 parts by dry weight of the organic acid.

In order to further improve the compatibility between the organic acid and the organic high molecular weight compound in addition to the color forming property, it may further be preferred to incorporate an aliphatic carboxylic acid and/or a polyvalent metal salt thereof.

Examples of such aliphatic carboxylic acids include a saturated monocarboxylic acid represented by the formula CnH~2n+-]_C00H, where n is a number, examples may be mentioned of valerian acid, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid or a petrochemically derived synthetic fatty acid, an unsaturated or cyclic mono-carboxylic acid represented by the formula C H„ - COOH, where n is a number and m is a number such as 1» 3, 5, 7 or 9, e.g., examples here are acrylic acid, croton -acid, oleic acid, elaic acid, erucic acid, linoleic acid, linolenic acid, eleostearic acid, phenylacetic acid or naphthylacetic acid, a mono-oxy fatty acid such as lactic acid, ricinoleic acid or oxystearic acid, a halogenated fatty acid such as α-dichloropalmitic acid, α-chloro-stearic acid and α,α- dichlorostearic acid, a polyfatty acid such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, metaconic acid, glutaconic acid, maleic acid e and citric acid as well as halogenated products thereof, phenoxyacetic acid, a core-substituted phenoxyacetic acid, maleic acid copolymers, an unsaturated fatty acid polymer or an unsaturated carboxylic acid copolymer other than rosin.

A metal salt of the above-mentioned aliphatic carboxylic acids can also be used for this purpose. Such compounds include salts of all the metals which can form salts with the above-mentioned fatty acids. The aliphatic carboxylic acids or metal salts thereof can preferably be used in amounts of less than 100 parts by torr weight in relation to 100 parts by torr weight of the organic acid and the organic high molecular compound together.

A coating composition can be prepared by dispersing the particulate mixture consisting of the organic acid and the organic high molecular weight compound, if necessary, with a suitable binder in water or a suitable organic solvent which does not readily dissolve the organic acid and the high molecular compound. Of such organic solvents, mention may be made of methanol, ethanol, isoranol, ethylene glycol and propylene glycol, as well as mixtures of these with water. Examples of binders include starch, casein, gelatin, gum arabic, polyvinyl alcohol, polyacrylamide, acrylamide-methylol-acrylamide seed copolymer, i acrylamide-mtd-acrylonitrile copolymer, methylacrylamide-acrylic acid ester copolymer, acrylamide-acrylic ester copolymer, acrylic acid-acrylic acid ester copolymer, melamine resins, urea resins, sodium polyacrylate, carboxymethylcellulose, carboxyethyl cellulose, natural rubber, synthetic rubber, polyacrylic acid ester, polymethacrylic acid ester,, polyvinyl acetate, vinyl acetate-ethylene copolymer, polypropylene, polystyrene, polyisobutylene, vinyl chloride-vinyl acetate copolymer, methyl cellulose, ethyl cellulose, nitrocellulose, cellulose acetate, phenolic resins, butyral resins, petroleum resins and alkyd resins.

The binders, and especially water-soluble binders, can be added together with a chemical binder to form water-insoluble binders during the reaction.

If an aqueous coating composition is desired, a water-insoluble binder can be used together with a suspension or an emulsion in water.

A carboxyl-modified polymer emulsion is particularly ..preferred.., because it is quite stable in coating and shows sufficient adhesiveness even in small amounts. Examples of such emulsions are carboxylated styrene-butadiene copolymer emulsions, carboxylated methyl methacrylate-butadiene emulsions and vinyl acetate-crotonic acid copolymer emulsions. In many cases, mixtures of two or more binders are used, and usually a suitable combination of a water-soluble and water-insoluble binder is used. . A coating composition can contain water-insoluble oxides, hydroxides and carbonates of a polyvalent metal and/or other mineral pigments. Particularly useful are metal compounds such as oxides, hydroxides

■ and carbonates of are polyvalent metals that have excellent color-forming properties in coexistence with the aromatic carboxylic acid. Such metal compounds are therefore quite effective when used in combination with certain aromatic carboxyl

acids which have hitherto been considered to have too many disadvantages in practice due to inactive color reaction and low color density. Suitable inorganic metal compounds are oxides, hydroxides and carbonates of metals such as magnesium, calcium, barium, zinc, titanium, aluminium, nickel, cobalt, manganese, iron, tin, chromium and palladium. Examples of typical compounds are magnesium oxide, calcium oxide, barium oxide, zinc oxide, aluminum oxide, tin oxide, magnesium hydroxide, calcium hydroxide, zinc hydroxide, aluminum hydroxide, tin hydroxide, magnesium carbonate, calcium carbonate and zinc carbonate.

The above-mentioned inorganic metal compounds which are usually termed "mineral pigments" have little color-forming ability in themselves, but nevertheless show a special "color-forming property in combination with the aromatic carboxylic acids. The above-mentioned specified metal compounds are therefore here indicated as "inorganic metal compounds" and distinguish thus differ from the usual mineral pigments. Other mineral pigments that can be used and which are different from the above-mentioned inorganic metal compounds can be exemplified by activated clay, acid clay, aluminum silicate, zinc silicate, tin silicate, a colloidal aluminum hydrosilicate zeolite, bentonite, kaolin and talc. These will in the present invention is referred to as "mineral pigment".

The composition according to the present invention can include the above-mentioned inorganic metal compound and mineral pigment in amounts from 1 to 10,000, preferably from 5 to 1,000 parts by torr weight in relation to 100 parts by torr weight of the aromatic carboxylic acid and/or a polyvalent metal salt thereof. It is understood that the coating composition may contain all or part of the inorganic metal compound and the mineral pigment incorporated in the particulate substrate consisting of the organic acid and the organic high molecular compound as mentioned above.

The pre-coated coating compositions for certain types of self-supporting copying paper further contain fine micro-*capsules" which envelop the color former.

The coating composition is applied to the surface

a coating in the usual way, e.g. using a knife, roller, blades or a printing press, or is printed on the substrate using an offset press or similar, or can be applied

using a so-called flexographic method. If the composition is of the type of an organic solvent, the printer anode itself is preferred, and the composition may further contain a plasticizer such as tributyl phosphate, dibutyl phthalate, dioctyl phthalate, butyl adipate and castor oil.

A paper of natural fibers, a paper of synthetic fibers or a film of synthetic polymers can be used as a substrate, although a paper of natural fibers is usually used. If necessary, the substrate can have a surface layer of a natural or synthetic high molecular compound.

Sensitized copy sheets according to the present invention have a number of advantages of the type mentioned below. The organic acid, because it is protected from the influence of heat, light and especially high humidity or water by means of the organic high molecular compound, can maintain a. stable color-forming ability for a very long time and completely prevents so-called "spotting". Consequently, you can use an organic acid with a relatively low molecular weight such as salicylic acid or et

of its polyvalent metal salts which were previously unsuitable for practical application.

The coating composition, due to its excellent mechanical stability and heat stability, can be kept in a perfect condition and the coating itself can be very easily carried out. Furthermore, it is possible to apply the composition to the substrate with the help of a coating device lasered on a paper machine, so that the printable copy sheets can be produced in a very economical way.

The particulate mixture consisting of the organic acid compound and said organic high molecular compound can be pulverized into fine powders with a uniform particle size of a few microns mechanically, e.g. by painting in ball mold. It is therefore possible to form a coating layer where the fine powder is homogeneously dispersed so that clear images are obtained without unclear parts ("bleeding").

The coating composition is usually applied in quantities of more than about 2 g/m 2 , and the upper limit is limited only for economic reasons.

The following examples illustrate the invention.

Parts are from here on stated as dry weight parts if nothing else is stated.

Example 1

100 parts of a thermoplastically modified xylene formaldehyde resin with a softening point of 110°C ("Nikanol S-100") was heated to 180°C, added 90 parts of zinc, 3,5-di(a,a-dimethyl)-salicylate under rowing and was dissolved. A mass was obtained by cooling and drying the mixture. The mass was roughly crushed and then pulverized with 200 parts of kaolin and 30 parts of a powdered silicic anhydride ("Carplex No. 80") in a ball mill for 15 hours. A particulate mixture with a particle size of approx. 3 ^u. To the total contents of the mold was added 40 parts soluble starch and 100 parts styrene butadiene copolymer latex (solids 50%) and 60 parts water and then

area. A coating composition was obtained. A sensitized sheet was prepared by applying the coating to the surface of a continuously running paper web with a weight of 50 g/m 2 in an amount of 10 g/m 2 dry weight, using a laboratory paper machine ("Rissar Paper Machine") equipped with a coating device of a similar type found on larger paper machines.

The composition was applied to the surface of a preheated paper band and excess material was recycled during the work. As a result of this, the composition was subjected to mechanical shear forces and at the same time the temperature reached 70°C at its highest, but the composition retained a markedly stable fluidity without an increase in viscosity.

Examples 2-1 to 2-14

100 parts α-methylstyrene-styrene copolymer with a molecular weight of approx. 1500 was produced by polymerizing approx. 60% by weight of α-methylstyrene and 40% by weight of styrene in the presence of thioglycollic acid were incorporated and fused with 200 parts each of the organic acid compounds given below, at temperatures from 150-190°C, whereby formed a homogeneous liquid phase. An easily crushable mass was obtained by cooling said liquid phase.

200 parts of each of the masses thus produced,

was crushed to an average particle size of approx. 200 µl, and was incorporated with one part formaldehyde sodium naphthalenesulfonate condensate ("Demol-N"), 600 parts water and 20 parts soluble starch, and passed through a ball mill. Finally, 40 parts of a styrene-butadiene copolymerization latex (50%

solids) added, whereby different compositions were produced.

Sensitized sheets were produced by applying each of the compositions to a substrate in amounts of approx. 7 g/m2 dry weight in the same way as stated in example 1. All the coated compositions had excellent mechanical stability and thermal stability during the actual coating.

Example 3-1 to 3-14

200 parts each of a mass produced in example 2 were crushed to an average particle size of approx. 200 ^u, in-

incorporated with 200 parts kaolin, 50 parts zinc oxide, 600 parts water and 40 parts of a soluble starch and one part "Demol-N"

(see example 2), and was then pulverized in a ball mill.

Finally, 100 parts of a carboxylated styrene-butadiene copolymer latex (50% solids) was added, to make various compositions.

Sensitized sheets were produced by applying each of the compositions to a substrate in an amount of 10 g/m 2 dry weight in the same manner as stated in Example 1. All compositions had excellent mechanical stability and heat stability of the same type as stated in Example 1.

Example 4

A coating composition was prepared in the same manner as in Example 1, except that 5 parts of zinc stearate were added together with 100 parts of "Nikanol S-100" (see Example 1) and 90 parts of zinc-3,5~di(a ,α-dimethylbenzyl)-salicylate.

A sensitized sheet was prepared from the composition in the same manner as indicated in Example 1.

Example 5

100 parts cc-methylstyrene polymer with an average molecular weight of approx. 1100 was heated to approx. 180°C together with 10 parts of zinc stearate and 60 parts of zinc 3-[4'-(a,a-dimethylbenzyl)phenyl]-5-(a,a-dimethylbenzyl)-salicylate, and melted down as a mass. This mass was cooled, crushed and coarsely crushed. The crushed product was added to 40 parts of powdered zinc silicate, 20 parts of polyacrylamide (degree of polymerization about 1000) and 500 parts of water, and was pulverized in a porcelain ball mill for about 20 hours. Finally, 60 parts of a styrene-butadiene polymerization latex was added - for the production of a coating composition.

A sensitized sheet was produced from the composition in the same way as stated in example 1. The coated composition had good mechanical stability and thermal stability during the actual coating. Example 6-1 to 6-14

100 parts of α-methylstyrene polymer (molecular weight about 1100) was mixed and melted with 150 parts of each of the organic acid compounds listed below at temperatures from 100 to 200°C. A mass was obtained by cooling and solidifying the resulting liquid.

Each of the masses was crushed into powders with a particle size of approx. 200 ^u. 200 parts of each of the pulverized masses were mixed with 50 parts of zinc oxide, 600 parts of water and 40 parts of a soluble starch and pulverized in a ball mill. Finally, 100 parts of a carboxylated styrene-butadiene copolymer latex (50% solids) was added. A sensitized sheet was produced from the coating composition by applying the composition to the substrate in the same way as in example 1. Each of the compositions had the same mechanical and heat stability as stated in example 1.

Example 7

100 parts polystyrene with a molecular weight of approx. 1000, 50 parts of aluminum 3-(oc,α-dimethylbenzyl)-5-cyclohexyl salicylate and 300 parts of kaolin were heated to 180°C and melted down as in 1. a lot. This mass was cooled and crushed. The mass was

coarsely crushed, and mixed with 520 parts of an aqueous solution containing 20 parts of polyvinyl alcohol and then pulverized in a ball mill for 20 hours. Finally, 20 parts of a styrene-butadiene copolymer latex (50% solids) were added, whereby a coating composition was produced.

A sensitized sheet was produced from the composition

in the same way as in example 1. The coating composition showed good mechanical stability and thermal stability in the same way as stated in example 1.

Example 8

100 parts of an oc-methylstyrene polymer with a molecular weight of approx. 1000, 50 parts of 3-cyclohexyl-5-(α,α-dimethyl)-salicylic acid, 3 parts of stearic acid and 30 parts of zinc oxide were heated to 170°C and melted down. The mass was cooled and blotted dry. It was then coarsely crushed and added to 500 parts of an aqueous solution containing 20 parts of starch and then pulverized in a ball mill for 10 hours. Finally, 50 parts of a styrene-butadiene copolymer latex (50% solids) were added, whereby a coating composition was produced.

A sensitized sheet was prepared from the composition

in the same way as stated in example 1. The composition had good mechanical stability and thermal stability in the same way as stated in example 1. Example 9

100 parts polystyrene with a molecular weight of approx. 2000 prepared by a polymerization in carbon tetrachloride and 100 parts of aluminum 3,5-di(α-methylbenzyl)-salicylate was melted down at approx. 150°C and cooled and crushed. The mass obtained was crushed into granules with a particle size of less than approx. 1000 ^u, added 400 parts kaolin and 100 parts zinc oxide and then pulverized in a ball mill for 10 hours. The entire finely powdered product was dispersed in a solution containing 200 parts water, 800 parts ethanol and 100 parts ethyl cellulose so that a black-like composition was formed.

A sensitized sheet was produced by printing the ink composition on a substrate which had a weight of 50 g/m<p >in an amount of 7 g/m dry weight using a normal printing press.

Example 10

100 parts of a styrene-allyl alcohol copolymer (monomer weight ratio 90:10, molecular weight approx. 3,000) and 200 parts of zinc 3,5-di-(α-methylbenzyl) salicylate were dissolved in 200 parts of acetone. The acetone was then evaporated, whereby a mass was obtained. The mass was coarsely crushed to a particle size of approx. 200 µl, and 200 parts of this product were mixed with 1 part "Demol-N" (see -Example 2), 600 parts of water and 20 parts of a soluble starch and were then pulverized in a pulverizer ("Attritor"). Finally, 40 parts of a styrene-butadiene copolymer latex (50% solids) were added, whereby a coating composition was produced.

A sensitized sheet was prepared using this composition in the same manner as indicated in Example 1.

Example 11

100 parts of styrene-allyl alcohol copolymer (monomer weight ratio 85:15, molecular weight approx. 1500) and 300 parts of zinc 3,5-di-(α-methylbenzyl)-salicylate were dissolved in 300 parts of acetone. The obtained solution was little by little added to a dispersion consisting of 2,500 parts water, 30 parts "Demol-N" (see example 2) and 500 parts kaolin while stirring, whereby a dispersion of a particulate substrate consisting of styrene- the allyl alcohol copolymer and zinc 3,5-di-(α-methylbenzyl)-salicylate. A sensitized sheet was prepared by applying the dispersion in a weight of approx. 7 g/m dry weight on a substrate with a weight of 50 g/m<2>.

Example 12

200 parts of a polystyrene emulsion (50% solids) were added to 100 parts of a 30% aqueous solution of sodium 3-(α,α-dimethylbenzyl)-5-methylsalicylate, heated to a temperature of 80°C and little by little added 500 parts of a 40% aqueous solution of stannous chloride while stirring. The reaction was further continued for 1 hour at a temperature of 90°C. The emulsified polystyrene particles contained tin-3-(α,α-dimethyl-benzyl)-5-salicylate. Then, with vigorous stirring, 150 parts of kaolin, 100 parts of water and 30 parts of a were added to the above-mentioned emulsion. soluble starch, whereby one was produced

coating composition.

A sensitized sheet was produced from the composition in the same manner as indicated in example 1.

Example 15-1 to 13-9

100 parts of zinc 3,5-di(a-methylbenzyl)-salicylate were melted down with 50 parts each of the organic high molecular weight compounds indicated below. The resulting mixture was cooled and solidified, whereby a mass was obtained.

Example No. Organic high molecular compound 13-1 Styrene-α-methylstyrene copolymer (monomer weight ratio 60:40, molecular weight 5,000)

13-2 Polystyrene (molecular weight 1,500)

13-3 Styrene-acrylonitrile copolymer (monomer weight ratio 80:20, molecular weight 2,000)

13-4 Vinyl chloride-vinyl acetate copolymer (monomer weight ratio 85:15, molecular weight 5,000)

13-5 Styrene-methyl methacrylate copolymer • (monomer weight ratio 80:20, molecular weight 2,000)

13-6 Diphenyl-formaldehyde polycondensation product.

(molecular weight 600) 13-7 Shellac

13-8 Polystyrene (molecular weight 1,500) 70 percent by weight and paraoctylphenol-formaldehyde polycondensa-■

Each of the above masses was coarsely crushed. 150 parts- . of each of the crushed products was mixed with 75 parts of kaolin, 35 parts of activated clay, 450 parts of water and 30 parts of a soluble starch and was pulverized in a ball mill. Finally, 75 parts of a styrene-butadiene copolymer latex (50% solids) were added, whereby a coating composition was formed. A sensitized sheet was produced from the composition in the same way as stated in example 1. The coating composition has very good mechanical stability and heat stability in the same way as stated in example 1.

For comparison with the above examples, an aqueous dispersion of an organic acid compound and with the composition indicated below was prepared separately.

Control 1:

Control 2:

Control 3:

Control 4:

A sensitized sheet was prepared by applying each

of the above dispersions on a substrate (50 g/m ) in an amount of from 7 to 10 g/m dry weight in the same way as indicated in example 1.

In order to confirm the effect of the sensitized sheets according to the present invention, a top sheet coated with microcapsules containing a color former was produced. The microcapsules were prepared as indicated e.g. in the U.S. patent no. 2,800,457 A description of the method is given below.

30 parts of an acid-treated gelatin was added to 470 parts of water and dissolved at 60°C. 3 parts of crystal violet lactone were dissolved in 100 parts of isopropylnaphthalene, heated to 60°C

and added the above-mentioned aqueous gelatin solution, which was then emulsified and dispersed under stirring so that oil droplets with an average particle size of 4-5 µm were formed. Then 300 parts of a 10% aqueous solution of gum arabic was added to the above-mentioned emulsion, a further 200 parts of water were added, after which the pH of the dispersion was adjusted in the range 4.-4.5 by adding acetic acid. The dispersion was cooled to 10°C, whereby a coacervate film was formed to which 10 parts of formaldehyde were added. After aging for 10 hours, a capsule mist was formed. persion. A top sheet was produced by applying the dispersion to the base paper (weight 50 g/m ) in a weight of approx. 5 g/m dry weight.

The effect of the sensitized sheets according to the present invention was confirmed in the following way. A sensitized sheet was subjected to the treatments mentioned below and a control sheet of the same type which was not subjected to any treatment was both placed under an upper sheet with encapsulated color former in such a way that the coated surface was in contact with the microcapsules , and a print was made using a typewriter. The stability of the color-forming ability to heat, light and humidity was observed by comparing differences with regard to the density of a developed color image on the treated sheet and the untreated sheet.

a) A sensitized sheet was placed in an environment with 90% relative humidity and a temperature of 50°C in

10 hours.

b) A sensitized sheet was placed at 100°C for 5 hours. c) A sensitized sheet was exposed directly to the sun

for 3 hours.

In addition to the above-mentioned samples, a sensitized sheet was also brought into close contact with an upper sheet in such a way that the coated surface was opposite the surface with the microcapsules. After immersion in water, the sheets were dried and separated. In the event that a sensitized sheet has weak resistance to water, the coated surface of the upper sheet will develop color and so-called "staining" occurs.

The results of the above tests are given in Table 1.....

In order to confirm the stability of the developed color image against light, heat, humidity and water, the following tests were carried out. The top sheet was placed over the sensitized sheet in such a way that the coated surface was in contact with the microcapsules and a print was produced using a typewriter. After resting for 24 hours, the sensitized sheet was subjected to the treatments described below, and one could

.observe a reduced density on the color image.

a) A sensitized sheet was placed at 90% relative humidity and 50°C for 10 hours. b) A sensitized sheet was placed at 100°C for 5 hours. c) A sensitized sheet was exposed to direct sunlight for 3 hours. d) A sensitized sheet was dipped in water and dried at normal temperature.

The results of the above samples are given in table 1.

Remarks:

Stability of color forming ability

A: maintained its original coloring. ability B: almost not impaired

C: severely impaired D: completely impaired

(color image could not be created)

Stability of developed color image

A: no color change

B: hardly bleached :

C: strongly bleached.

D: bleached or discolored

Color iridescence in the image

A: 'hey'

B: means

C: extremely low-

Claims (2)

1.. Sheets for use in a pressure-sensitive copying system, sensitized with a coating, for producing color upon contact with a chromogenite material, which coating contains at least one. .acidic compound selected from aromatic' carboxylic acids and polyvalent metal salts thereof, characterized by the 'at' coating, - contains a homogeneous mixture, in particulate form of:.'., a) . ' 100 parts by weight of acid" compound, and ... '. \ 'b) - 5-300. parts by weight, of at least one solid. "compound, with molecular weight above 400,. chosen from polystyrene, styrene copolymers-methyl-■ styrene polymers, α-methylstyrene copolymers, polyvinyl chloride, vinyl chloride copolymers,. vinylidene chloride copolymers, polychloropreh, cyclopentadiene polymers, cyclopentadiene copolymers, acrylic ester--polymers, acrylic ester copolymers, acrylic acid copolymers, methacryl- . ester copolymers, methacrylic ester copolymers, methacrylic acid copolymers, vinyl acetate polymers, vinyl acetate copolymers, such as ethylene-vinyl acetate copolymers, acrylonitrile copolymers, acrylamide copolymers, allyl alcohol polymers, benzyl chloride polycondensation products, benzyl chloride copolycondensation products, metaxylene formaldehyde condensates, diphenyl formaldehyde condensates and diphenyl formaldehyde condensates ' . metaxylene formaldehyde condensation products.- 2. Sheet according to claim 1,' c a r a c t e r i s. e,r t . w e d that at least one aliphatic carboxylic acid or a polyvalent metal salt thereof is present and incorporated in the particulate mixture consisting of said organic acid compound and said high molecular compound..