NO133656B - - Google Patents

Description

The present invention relates to a halogen-free solvent for basic, colourless, chromogenic Targestof precursor material and/or for acid-reactive polymer material used as isolated microdroplets in the coating in pressure-sensitive copying materials - In these materials, at least one of two color-forming

-reactants in solution in the form of said microdroplets. One of the color-forming reactants is -a precursor for a basic chromo-

gent dye and another reactant is an acid-reactive polymeric substance that develops the color of the chromogenic dye precursor when the two reactants react with each other by breaking the insulating medium between them. Isolation of the liquid microdroplets is preferably carried out by encapsulating the droplets with polymeric film material.

In this area, the production of pressure-sensitive copying material, including liquid-containing microcapsules, in commercial practice crystal violet lactone (Crystal Violet Lactone ~ CVL) has been used as the chromogenic agent f-for Løper, and

an acidic co-reactant such as attapulgite clay or an oil-soluble para-substituted phenolaldehyde novolak resin and a liquid solvent which is at least partially a halogenated aromatic liquid, especially mixtures of chlorinated biphenyls. halogen

aromatic liquids have a low vapor pressure and good solubility and are well retained in gelatin films. the most used capsule wall material. Halogenated aromatic compounds have therefore proved suitable as solvents in pressure-sensitive copying material of the type described. However, it has now been found that the rate of fading of CVL copies made in this way, on exposure to air and light, increased in the presence of halogen-containing solvents- The search for non-halogenated solvents which have the same advantages as chlorinated biphenyls

but without the disadvantage of faster bleaching, has led to the aromatic solvent systems of the present invention, which comprise isopropyl biphenyl.

Isopropylbiphenyl means a compound or mixture of compounds with the structure:

The isopropyl group can be attached to the benzene ring in the ortho-,.

the meta or para position. Synthetic methods that are often used form a mixture of at least two of the three possible isopropyl biphenyls. Of particular use according to the invention is a mixture in which meta-isopropylbiphenyl and para-isopropylbiphenyl! is present in the greatest quantity. The ta isomers seem to work equally well in the copying system according to the invention and better than ortho-isopropylbiphenyl, either alone or in combination.

It has been found that isopropyl biphenyl gives better print intensities and better fading resistance than. higher alkylated biphenyls such as butylbiphenyl, amylbiphenyl, hexylbiphenyl, decylbiphenyl, diisopropylbiphenyl and triisopropylbiphenyl. Increasing alkyl content in alkylated biphenyls also generally leads to poorer solubility, at least when CVL is the chromogen to be dissolved. However, a certain amount of higher alkylated biphenyls can be tolerated as impurities in the isopropyl biphenyl. When the contaminants are polyisopropylbiphenyls, that is usually diisopropylbiphenyl with traces of triisopropylbiphenyl, should not. over 55% by weight of it. total biaryl content" be such higher alkylated types. Preferably at most 25 to 30% of the total biaryl content is polyisopropylbiphenyl. Unalkylated biphenyl, i.e. biphenyl itself, can also be tolerated as a contaminant in the isopropylbiphenyl. Biphenyl as a contaminant appears - not to damage the iso-propylbdphenyl's desired properties,, but when the amount of biphenyl amounts to more than about 10% of the total biaryl content, the smell of biphenyl usually makes such copying material unsuitable for marketing. By "total biaryl content" is meant the amount of -isopropylbiphenyl present together with its impurities, polyisopropylbiphenyl and biphenyl. By "polyisopropylbiphenyl" is meant biphenyl with two or more isopropyl groups substituted on the molecule. According to the present invention, there is thus provided a halogen-free solvent for basic, colorless, chromogenic dye precursor material and/or for acid-reactive polymer material used as isolated microdroplets in the coating in pressure-sensitive k opiate materials, characterized by the fact that the solvent essentially consists of biaryl compounds selected from biphenyl, isopropylbiphenyl and polyisopropylbiphenyl, where at least 30% of the total biaryl content is isopropyl ifenyl, at most 55% is polyisopropylbiphenyl and ■ at most 15% is biphenyl, and that the solvent possibly also includes a higher-boiling, saturated aliphatic hydrocarbon oil. Non-halogenated diluents can be added to the isopropylbiphenyl compound without adverse effect on

■the copying material. High-boiling aliphatic hydrocarbons and

<C>10~ C₁-alkylbenzenes have been used successfully as diluents for iso<p>ro<p>yl biphenyl. Since these diluents are usually cheaper than isopropyl biphenyl, it is advantageous to use them from an economic point of view. The degree of solubility of the selected colorless, chromogenic dye precursor in the selected diluent determines the maximum amount of

such diluent -as may be used. If the isopropyl biphenyl is to be diluted with other oils, the diluted isopropyl biphenyl should be able to dissolve "at least 1% and preferably 1.5% or more of the selected dye precursor. When CVL is the selected

dye precursor, preferred diluents are saturated aliphatic hydrocarbons with a destination range within 160 to 288°C, which can be added to the isopropyl biphenyl in such a large amount that they amount to approx. 1/3 of the total weight of the CVL dissolution medium, and C 1 -C 4 -alkylbenzenes may be used in an amount up to 2/3 of the total weight of the dissolution medium.

In addition to the preferred diluting hydrocarbons mentioned above, one can of course add many oils which are known in the field as suitable solvents for the internal phase of the capsules,

in combination with isopropyl biphenyl, provided that the former is not halogenated, that they are at least partially miscible with isopropyl biphenyl, so that a single phase is obtained in the quantities used, and that they are not chemically reactive with isopropyl biphenyl or other components of the marking fluid. E.g. are low molecular weight aromatic hydrocarbons such as xylene and toluene, organic acid esters such as fatty acid esters and phthalic acid esters, phosphate esters such as dibutyl phosphate, dioctyl phosphate and dicresyl phosphate, and esters such as diphenyl oxide are all suitable for use as diluent oils.

Another unexpected advantage of the copying material according

to the invention is that the color formation strength is also greater than in known systems which include chlorinated biphenyls. This makes it possible to use less marking fluid per surface area for development of the same amount of colour. The color formation effect of the copying material coated with microcapsules having an inner phase consisting of 1.7 # CVL dissolved in a 2:1 mixture of isopropyl biphenyl and saturated hydrocarbon is 16% greater than the color formation effect of the copying material coated with microcapsules having an inner phase consisting of 1, 5$

CVL dissolved in a 2:1 mixture of chlorinated biphenyl (with 42$ > chlorine content) and saturated hydrocarbon. This increased effect means savings in raw materials and reduced coating weight in the finished product.

Isopropyl biphenyl solvents with the following composition have been investigated and found to provide an improvement over chlorinated biphenyls:

The preferred composition for use according to the invention is c<a,>49.5% meta-isopropylbiphenyl, 28% para-isopropylbiphenyl, 22% polyisopropylphenyl, 0.5% biphenyl. This preferred composition is best represented by samples "D" and "N" above.

Samples of isopropyl biphenyl with approx. $75 polyisopropyl biphenyl contamination in mbination with approx. 25% isopropyl biphenyl (a mixture of meta- and para-isomers) in a 2:1 mixture with a saturated hydrocarbon as the internal phase for dissolving CVL gave somewhat weaker impressions on phenolic resin-sensitized paper than solutions of CVL in the ratio 2: l-chlorinated biphenyl/saturated hydrocarbon oil, and showed no significant improvement in bleach resistance.

Isopropyl biphenyl grades for use according to the invention can be obtained commercially or can be synthesized by Friedel-Craf i. - alkylation of biphenyl.

Dye precursors other than CVL that can be dissolved in isopropyl biphenyl for encapsulation include all colourless, chromogenic dye precursors listed in Norwegian patent no, 112,873

The same patent also deals with examples of phenolaldehyde resins suitable for use as co-reactants for developing color in the dye precursor. In general, preferred resins are oil-soluble para-substituted phenol-formaldehyde-novolac resins.

Capsule wall materials and capsule production are not decisive for the present invention. Suitable methods for producing capsule-coated copying sheets can be found in the above patent.

Other methods for isolating labeling microdroplets can also be used here, such as e.g. initiation of the microdroplets in a dried emulsion film.

Production and use of the copying material containing isopropyl biphenyl is detailed in the following examples.

All quantities and percentages are on a weight basis if

nothing else is listed.

Example 1.

Encapsulation of t^ VL solution in isopropyl biphenyl -

A solution of CVL, 1.7%, in isopropyl biphenyl, sample "D" from Table I, was used as the internal phase in the capsules. The following composition was emulsified in a Waring mixer at 55°C into microdroplets of Omikron diameter:

150 g inner phase

150 g 10 #-ig gelatin at pH 6.5

62 g deionized water.

Coamination was carried out by adding 10% gum arabic cum solution, 10 g of 5 µg polyvinyl methyl ether/maleic anhydride (PVM/MA) and 60-0 g of deionized water, with continued stirring at 55°C. With constant stirring and maintenance of said temperature, the mixture was treated with sufficient 20% sodium hydroxide solution to adjust the pH to 9%, after which 12.5 ml of 14% acetic acid was added dropwise. The mixture was cooled slowly with continued stirring to 12°C and treated with 7.5 ml of 25 µg glutaraldehyde. After 4 hours of stirring, 12.0 ml of basic 5 #-ig PVM/MA -(-pH 9.0) was added dropwise, and stirring was continued for 2.5 hours while gradually warming to room temperature.

The pH of the mixture, which was then a suspension of microcapsules, was finally adjusted to 9.5 with 20 tf> sodium hydroxide. The microcapsules can be used as an aqueous suspension or can be isolated by filtration and air dried.

Example 2.

Encapsulation of CVL solution in isopropyl biphenyl hydrocarbon oil.

According to the method from example 1, microcapsules were produced where a 2:1 mixture of isopropyl biphenyl and saturated hydrocarbon oil (destination range 188-260°C) was used instead of isopropyl biphenyl in the previous example.

Example 3.

Encapsulation of CVL solution in isopropyl biphenyl alkylbenzene.

According to the method from example 1, microcapsules were produced in which the isopropyl biphenyl from this example was replaced with a 1:2 mixture of isopropyl biphenyl and mono-C 1 to C 3 -alkylbenzene.

Example 4.

Encapsulation of phenolic resin solution.

The procedure in Example 1 was generally followed, and a 10 µg solution of para-phenylphenol-formaldehyde-novolac resin was encapsulated in a 2:1 mixture of isopropyl biphenyl and xylene. The original emulsion consisted of 180 g of internal phases, 191 g of 11 µg gelatin at pH 4.3 and 15.8 g of deionized water. Coamination was carried out by adding 127 g 11 µg gum arabic solution, 135 g 5 µg PVM/MA and 817 S deionized water. In the final step, 21 ml of 14 µg acetic acid, 10 ml of 25 µg glutaraldehyde and 20 ml of basic 5 µg PVM/MA were added instead of the amount stated in example 1. The final stirring times were also changed: 16 hours.after the glutaraldehyde addition and one hour after the last basic PVM/MA addition.The adjustment of pH to 9.5 was omitted.

Example 5•

Encapsulated icopy sheets.

An aqueous slurry was prepared from the following constituent parts which were stirred together:

Sheets of paper were coated with the above slurry with a Mayerstav no. 15 Pg gave a dry coating weight of approx. 5.2 g/m2.

Coatings with capsules of Example 1, 2 or 3 produced copy sheets that showed intense blue characters when pressed against acid-sensitized receiver sheets. These characters were stronger and more fade resistant.

(to light and air) than similar signs on sheets coated with chlorinated biphenyl hydrocarbon oil as the internal phase solvent for CVL.

Similar results were obtained when coated sheets with capsules as in Example 4 were used as transfer sheets against a receiver sheet which was sensitized by dipping in an acetone solution containing a colorless chromogenic dye precursor and dried. Among the colorless, chromogenic dye precursors used for this sample were CVL, malachite green lactone, N-(2,5-dichlorophenyl)leucauramine, N-benzoylauramine, methyl red, 4-aminoazob.enzene, 8' -methoxybenzo-indolinospiropyran and Rhodamine B-lactam.

Claims (6)

1. Halogen-free solvent for basic, colourless, chromogenic dye precursor material and/or for acid-reactive polymer material used as isolated microdroplets in the Delegget in pressure-sensitive copying materials, character t i. =s -e r t v e d 'that the solvent consists essentially of biaryl compounds selected from biphenyl, isopropylbiphenyl and polyisopropylbiphenyl, where at least 30% of the total biaryl content is isopropylbiphenyl, at most 55% is polyisopropylbiphenyl and at most 15% is biphenyl, and that the solvent optionally also comprises a higher-boiling saturated aliphatic hydrocarbon oil. . 2. Halogen-free solvent according to claim 1, characterized in that the isopropylbiphenyl compound is made up of a mixture of isomeric compounds, namely meta-isopropylbiphenyl and para-isopropylbiphenyl. 3- Halogen-free solvent according to claim 1, characterized in that the ratio between isopropyl biphenyl and hydrocarbon oil is 2:1. 4, Halogen-free solvent according to claims 1-3, ■characterized in that the solvent has been added to a small amount of a mono-C₂₂-C₂₂-alkylbenzene. 5. Halogen-free solvent according to claim 4, characterized in that the alkylbenzene compound is mono-C-L1-C^2-alkylbenzene. 6. Halogen-free solvent according to claims 1-5, characterized in that the total biaryl content consists of about 49 15-J£meta-isopropylbiphenyl, about 28% para-isopropylbiphenyl, about 22% polyisopropylbiphenyl and about 0.5% biphenyl.