EP0000903B1 - Carbonless copying paper and manufacture thereof - Google Patents

Description

Reaction carbon papers are known (see M. Gutcho, Capsule Technology and Microencapsulation, Noyes Data Corporation 1972, pages 242-277; G. Baxter in Microencapsulation, Processes and Applications, edited by JE Vandegaer, Plenum Press, New York, London, pages 127 -143).

Reaction copy papers are also known from US Pat. No. 3,432,327. This is understood to mean papers in which two layers are in contact with one another, each of which contains a color-forming component which reacts with the other to form a dye. At least one of the color formation components is in the form of microcapsules, which break when a writing tool is pressed and release the encapsulated component for reaction with the second. The two color-forming layers can be applied one above the other on a paper surface or separately on two paper surfaces in contact with one another.

According to US Pat. No. 3,432,327, phase interface polymerization, a polyreaction at the phase interface of a hydrophilic and a hydrophobic liquid, is used for the production of the microcapsules. According to the US patent, the reaction to the dye must take place in the hydrophilic medium. Therefore, a color-forming component is first dissolved in a hydrophilic liquid, for example water, and then the first component of the capsule wall material is added to this solution. The second component of the capsule wall material is dissolved in a hydrophobic liquid (oil, paraffin, aromatic solvent), and then the hydrophilic solution is dispersed in the hydrophobic. The microcapsule then forms from the two capsule wall components at the phase interfaces of the dispersed hydrophilic droplets.

The second color forming component can also be encapsulated; as a rule, however, it is not encapsulated.

A large number of pairs of suitable color forming components are given in the US patent; it may a. for inorganic salts (e.g. potassium hexacyanoferrate 11 - ammonium iron (III) sulfate), colored metal complexes (e.g. diacetyl-dioxime-nickel acetate) and organic dyes (e.g. bromocresol purple sodium hydroxide).

Capsule wall-forming components are also given in large numbers, for example the combination of certain selected diisocyanates and water, diol or diamine.

The operation of US Patent 3,432,327 is directed to encapsulating a solution of a color former in a hydrophilic solvent, preferably water.

However, this is a crucial disadvantage, because capsule films impermeable to water have so far been practically impossible to produce. Thus, these capsules are not stable in storage because they dry out after a more or less short time. Carbonless papers made from it thus quickly lose their carbonless ability.

German Offenlegungsschrift 23 11 712 also discloses the use of reaction products of di- or polyols with a molecular weight of 400-10,000 and di- or polyisocyanates as isocyanate components in microencapsulation. Map can thus encapsulate pre-dye solutions for carbonless papers; these capsules are not impermeable to the mostly aromatic and alkylaromatic solvents necessary for the process, although this is absolutely necessary for the effect of the reaction carbonless papers. They also tend to agglomerate very strongly. Capsule agglomerates cause considerable disruption because individual capsules are destroyed during the manufacture of the paper and a stained paper is thus obtained. Under unfavorable conditions, the writing performance of the papers is even significantly reduced. You therefore need individual capsules for carbonless papers that do not tend to agglomerate.

Finally, it is known from DE-OS 22 51 381 to include color formers in capsules, the walls of which consist of polyurea. On page 12 it is stated that good results are not always obtained, but especially when using polyisocyanate adducts or polyamine adducts. In the specifically stated cases, however, the tightness and the aging resistance of the microcapsules are insufficient.

• (1.) müssen für den Farbbildner und sein Lösungsmittel undurchlässig sein. Durchlässigkeit für den Farbbildner führt zur Verfärbung, Durchlässigkeit für das Lösungsmittel zum Eintrocknen des Kapselinhalts und damit zur Wirkungslosigkeit;
• (2.) dürfen erst unter dem Druck des Schreibgerätes zerbrechen. Die Kapselwand muß also andersartige Belastungen überstehen;
• (3.) sollen möglichst als individuelle Teilchen vorliegen und nicht als größere Agglomerate;
• (4.) müssen sich leicht auf die Papieroberfläche aufbringen und sofort fixieren lassen. Dazu müssen sie so temperaturstabil sein, daß sie Temperaturen bis zu 100°C beim Trocknen unbeschadet überstehen.

The microcapsules for the production of carbonless papers

• (1.) must be impermeable to the color former and its solvent. Permeability to the color former leads to discoloration, permeability to the solvent dries out the capsule content and thus makes it ineffective;
• (2.) may only break under pressure from the writing instrument. The capsule wall must therefore withstand other types of stress;
• (3.) should exist as individual particles if possible and not as larger agglomerates;
• (4.) must be easy to apply to the paper surface and can be fixed immediately. To do this, they must be so temperature-stable that they can withstand temperatures up to 100 ° C when drying without damage.

Furthermore, it is advantageous to use as little shell material as possible and to make the capsule walls as tight as possible against external influences, in particular against oxygen, exposure to light and acids or bases.

worin R einen Alkylenrest mit 2 bis 10 C-Atomen bedeutet und, andererseits, einem Diamin. Die aus dem Reaktionsprodukt resultierenden Kapselmembranen erfüllen in hervorragender Weise die oben angegebenen Anforderungen, wenn hydrophobe organische Lösungen der Farbbildner eingekapselt werden.The invention is based on the knowledge that walls of microcapsules containing color former solutions for carbonless papers are obtained from, on the one hand, diisocyanates of the formula (I)

wherein R is an alkylene radical having 2 to 10 carbon atoms and, on the other hand, a diamine. The capsule membranes resulting from the reaction product excellently meet the requirements specified above when hydrophobic organic solutions of the color formers are encapsulated.

worin R einen AlkyJenrest mit 2 bis 10 C-Atomen bedeutet, und einem Diamin.The invention relates to a carbonless reaction paper which contains a solution of a color former in microencapsulated form, the color former being encapsulated as a solution in a hydrophobic organic solvent, characterized in that the capsule walls are made from the polyaddition product of a diisocyanate of the formula (I)

where R is an alkylene radical having 2 to 10 carbon atoms, and a diamine.

Another object of the invention is the use of a solution of a color former in a hydrophobic, organic solvent as the core material in microcapsules, the walls of which consist of the polyaddition product of a diisocyanate of the formula (I) and a diamine, for the preparation of carbonless reaction papers.

In addition to those already mentioned, there is a further advantage when using these isocyanates because of the excellent solubility in many solvents which are suitable for the solution of the dye precursors. This gives you a degree of freedom in the choice of solvents, which is particularly important with regard to environmental pollution. In this way, the most suitable solvent for the solution of the dye and at the same time the least polluting solvent can be optimally selected by combination.

The diisocyanates of the formula (I) are derivatives of 2,4,6-triketo-1,3,5-oxadiazine with two free isocyanate groups. The compounds in which the radicals R are from butane, hexane and octane are particularly suitable descended. The n-hexane radical is particularly preferred. The products and their manufacture are known from DE-AS 1,670,666.

• Äthylendiamin-(1,2), Bis(3-aminopropyl)-amin, Hydrazin, Hydrazinäthanol-(2), Bis-(2-methylaminoäthyl)-methylamin, 1,4-Diaminobenzol, 4,4'-Diaminodiphenyl-methan, 1,4-Diaminocyclohexan, 3-Amino-1-methyl-aminopropan, N-Hydroxyäthyläthylendiamin, N-Methyl-bis(3-aminopropyl)-amin, 1,4-Diamino-n-butan, 1,6-Diamino-n-hexan, Äthylen-(1,2)-diamin-N-äthan-sulfonsäure (als Alkalisalz), 1-Aminoäthyläthylendiamin-(1,2), Bis-(N,N'-aminoäthyl)-äthylendiamin-(1,2).

Suitable diamines are aliphatic primary or secondary diamines such as:

• Ethylenediamine (1,2), bis (3-aminopropyl) amine, hydrazine, hydrazine ethanol (2), bis (2-methylaminoethyl) methylamine, 1,4-diaminobenzene, 4,4'-diaminodiphenylmethane, 1,4-diaminocyclohexane, 3-amino-1-methylaminopropane, N-hydroxyethylethylenediamine, N-methyl-bis (3-aminopropyl) amine, 1,4-diamino-n-butane, 1,6-diamino-n -hexane, ethylene- (1,2) -diamine-N-ethane-sulfonic acid (as alkali salt), 1-aminoethylethylenediamine- (1,2), bis- (N, N'-aminoethyl) -ethylenediamine- (1,2 ).

Color formers are essentially colorless, basic products that have different chromophoric groups. Examples of these are bis (p-aminoaryl) phthalides, leucoauramines, acylauramines, α, β-unsaturated aryl ketones, basic monoazo dyes, rhodamine B-lactams such as the N- (p-nitrophenyl) rhodamine B-lactams, by amino groups substituted polyarylcarbinols and their reaction products, for example their esters or ethers and various heterocyclic spiranes. Preferred compounds are 3,3-bis (p-dimethylaminophenyl) -6-dimethylamino-phthalide (crystal violet lactone). Benzoyl leukomethylene blue and derivatives from Michlers Hydrol, especially the p-toluenesulfinate from Michlers Hydrol.

Solvents for the basic color former component (dye precursor) and for the diisocyanates are generally aromatic hydrocarbons, which can also be substituted by alkyl or halogen.

Examples are chlorinated diphenyls, dodecylbenzene, mixtures of partially hydrogenated and unhydrogenated terphenyls, isopropyldiphenyl, diisopropylbenzene, ethyl benzoate, mixtures of diphenyl and diphenyl ether, phthalic acid butyl ester, aralkyl or diaryl ethers, the xylenes in aromatics and aromatics. The solvent for the diamines is generally water.

When writing the reaction carbonless papers, the leaking core material meets the receiver layer, which has a coating on which dyes are formed from the colorless dye precursors, which now make the copy appear. Coating materials are natural and synthetic products such as kaolin, attapulgite, montmorillonite, concreteite, acidic bleaching earth or phenolic resins. You can e.g. in the donor layer, i.e. the microcapsule layer, acid-activated dyes and acid-reacting components in the receiver layer.

The microcapsules can be produced in various ways. So you can first dissolve the diisocyanate and the dye precursor in a suitable solvent and emulsify this organic phase in an aqueous diamine solution, which may optionally also contain protective colloids. It is also possible to first emulsify the organic phase with or without surfactants and protective colloids in water to a desired particle size and only then to add the diamine necessary for the capsule wall formation to the aqueous phase.

To emulsify and stabilize the emulsion formed, emulsifying agents are added to the aqueous phase. Examples of such products acting as protective colloids are carboxymethyl cellulose, gelatin and polyvinyl alcohol. Examples of emulsifiers are oxyethylated 3-benzylhydroxybiphenyl, reaction products of nonylphenol with different amounts of ethylene oxide and sorbitan fatty acid ester.

The course of the capsule wall-forming polyaddition can be followed on the basis of the amine consumption. After the free isocyanate groups have been completely reacted, the oxadiazine ring of the isocyanate can be opened by increasing the temperature, a new isocyanate group being formed which can react with the amine already used or with another amine with crosslinking and curing of the polyaddition product.

The microcapsules can be produced continuously or batchwise. Dispersing devices which generate a shear gradient are generally used. Examples include blade, basket, high-speed stirrers, colloid mills, homogenizers, ultrasonic dispersers, nozzles, jet nozzles, and Supraton machines. The strength of the turbulence during mixing is primarily decisive for the diameter of the microcapsules obtained. Capsules from 1 to 2000 µm in size can be made. Capsules with diameters of 2 to 20 μm are preferred. The capsules do not agglomerate and have a narrow particle size distribution. The weight ratio of core material to casing material is 50-90 to 50-10.

The pressure-sensitive carbonless papers are produced in a known manner (see M. Gutcho, Capsule Technology and Microencapsulation, Noyes Data Corporation, 1972, pages 242-277). The microcapsule suspensions obtained primarily contain 10 to 35% by weight of capsules. They need something to cream as long as they do not contain any binding agent. This can be used for concentration. The preferred capsule size is around 10 µm. The homogenized capsule suspensions, provided with binders and optionally inert fillers such as talc or kaolin, can be applied manually with a floral wire squeegee or mechanically with an air brush in application quantities of 4-8 ₉₁ m ² on base paper (for example from 40 to 100 g / m ² ). The coating of base papers is described in German Offenlegungsschriften 1,934,457 and 1,955,542. The papers coated in this way contain the first color-forming component; they are called encoder components.

The donor component is generally the back of the top sheet for carbonless sets. The front of the next sheet is coated with the second coloring component. This layer is called the slave component. In the case of carbonless copies, the slave component is the top of the second sheet of paper. In the case of multiple copy sets, the following encoder sheets must have a slave coating on the opposite side. The production of such receiver layers is known and is also described in German Offenlegungsschriften 1,934,457 and 1,955,542.

example 1 (a) Manufacture of the turning material

2000 g of n-hexane-1,6-diisocyanate are mixed with 1 g of tri-p-tolylarsine oxide in a 2.7 l autoclave and stirred at 50 ° C. for 8 hours at a CO ₂ pressure of 3 atm.

Here 17.5 l of carbon dioxide are absorbed. The reaction is interrupted by adding 2 g of phosphorus trichloride and the reaction product is separated from the unreacted starting product in a thin-layer evaporator (two passes, heating temperature 180 ° C. at 1 torr).

1957 g of oxadiazinone with an NCO value of 19.0% and a viscosity of 2480 cp / 50 ° C. are obtained.

The IR spectrum shows the characteristic carbonyl absorption bands at 5.5 to 5.71 and 5.82 µm.

(b) encapsulation

0.75 g of crystal violet lactone and 0.25 g of N-benzoyl-leukomethylene blue are dissolved in 25 g of solvent naphtha (BV Aral's aromatic mixture of xylene, cumene, tuluene and other naphthenic oils) with stirring and heating to 70 ° C.

After the solution has cooled, 5 g of the oxadiazinone described in Example 1 (a) are added and dissolved.

The homogeneous organic phase is then emulsified in 300 g of water, which is 1.5 g. Mowiol 56-98 (polyvinyl alcohol from Hoechst AG) as an emulsifying agent.

A Kotthoff mixing siren is used for emulsification (8900 rpm, 1 l beaker).

After an emulsification time of approx. 1 minute, the mixing siren is replaced by a Lenart-Rapid laboratory stirrer (500 rpm). At the same time, a solution of 0.7 g of 1-aminoethylethylenediamine-1,2- (diethylenetriamine) in 70 g of water is added to the batch. With constant stirring, the batch is quickly heated to 70 ° C. and kept at this temperature for about 1 hour. The heating phase is only used to form a casing that is as stable as possible.

The diameter of the resulting microcapsules is in the order of 3-25 µm.

Example 2

The organic phase is prepared as described in Example 1 (b) with the change that 25 g of Solvesso 200 (aromatic mixture from Esso AG) are used as the solvent.

The encapsulation and aftertreatment is also carried out as described in Example 1 (b), with the change that 0.7 g of ethylenediamine in 70 g of water are added as the amine component to the outer phase.

The microcapsules are 3-25 µm in size.

Example 3

0.75 g of p-toluenesulfinate from Michlers Hydrol as the coloring component is dissolved in 25 g of phthalic acid di-n-butyl ester with stirring and heating to 80 ° C.

After the solution has cooled, 5 g of the oxadiazinone described in Example 1 (a) are added and dissolved.

The resulting organic phase is encapsulated and post-treated as described in Example 1 (b). 0.7 g of diethylenetriamine in 70 g of water are used as the amine component.

The resulting microcapsules have a diameter of 2-20 µm.

Example 4 (a) Manufacture of the wall-forming material

280 g of 1,4-tetramethylene) diisocyanate are saturated by introducing them with dry CO ₂ gas and, with stirring and further introducing carbon dioxide at 60 ° C., with 0.7 g of tri-n-butylphosphine (0.25% ) offset. After 2 hours, the NCO value has dropped to 53.8%. The reaction mixture is separated in a thin-film evaporator (heating temperature 180 ° C. at 1 torr), 219 g of 1,4-tetramethylene diisocyanate being recovered and 54 g of a viscous oil being obtained. This shows the bands characteristic of isocyanate group-containing oxadiazinetriones in the IR spectrum (4.4; 5.48; 5.71; 5.83; 6.93; 7.06 µm), and has an NCO value of 20.2% on and a molecular weight of 375.

(b) encapsulation

In 25 g of a mixture of 70 parts of Santosol 340 (partially hydrogenated terphenyl from Monsanto) and 30 parts of Solvesso 200 (aromatic mixture from Esso AG), 1.1 g of crystal violet lactone are dissolved at a temperature of 80 ° C. with stirring.

After the solution has cooled, 5 g of the oxadiazinone described under 4 (a) are added and dissolved. The solution, which is the organic phase, is then emulsified in 150 g of water which contains 0.75% Mowiol 26-88 (polyvinyl alcohol from Hoechst AG) as an emulsifying aid. A Kotthoff mixing siren is used for emulsification (8900 rpm, 500 ml beaker, stirring time approx. 1 minute). After the emulsification, a solution of 0.9 g of 1-aminoethylethylenediamine-1,2 (diethylenetriamine) in 50 g of water is added to the mixture, and the mixing siren is then replaced by a Lenart-Rapid laboratory stirrer (500 rpm). The stirring time is approx. 1 hour at 60 ° C.

The microcapsules are obtained with a diameter of 1-35 µm.

Example 5

A microcapsule dispersion with about 30% capsule content can be produced with the aid of an ultrasound homogenizer (type Minisonic from Ultrasonics) with a solution of 4.5 parts of crystal violet lactone and 17 parts of the oxadiazinone described in Example 1 (b) Perform 75 parts of Santosol 340 (partially hydrogenated terphenyl from Monsanto and 25 parts of Solvesso 100 (Esso AG) as the organic phase.

150 parts of the organic phase to 250 parts of aqueous phase are used for emulsification. The aqueous phase contains 0.5% Mowiol 26-88 and 0.1% Tween 80 (emulsifier from Atlas Chemie) as an emulsifying aid.

In total, the two phases or the emulsion produced therefrom are passed 5 times through the ultrasonic homogenizer. Immediately afterwards, the resulting emulsion is transferred to a beaker and swiftly stirred with a laboratory stirrer (type Lenart-Rapid, 500 rpm) the amount of ethylenediamine corresponding to the NCO value of the oxadiazinone used stoichiometrically added (as an aqueous 4% solution).

The resulting microcapsule dispersion is stirred at room temperature for about 1 hour. The microcapsules obtained are in the range of 1-30 µm in diameter.

Example 6

0.75 g of p-toluenesulfinate from Michlers Hydrol is dissolved in 25 g of ethyl benzoate with stirring and heating to 80 ° C.

After the mixture has cooled, 5 g of the oxadiazinone described in Example 1 (a) are added.

The resulting organic phase is with the aid of a Kotthoff mixing siren at 8900 rpm. emulsified in 300 g of water, which contains 0.5% Mowiol 56-98 as an emulsifying aid.

After a mixing time of about 40 seconds, a solution of 0.7 g of diethylenetriamine in 70 g of water is added to the mixture. After about 1 minute of emulsification, the mixing siren is replaced by a laboratory stirrer (Lenart-Rapid type, 500 rpm) and the microcapsule dispersion is kept at 70 ° C. for about 1 hour with stirring.

The microcapsules have a diameter of 3-25 µm.

Claims (2)

1. Pressure-sensitive copying paper, which contains a solution of a dye-precursor agent in micro- encapsulated form, wherein the dye-precursor agent is encapsulated as a solution in a hydrophobic organic solvent, characterised in that the capsule walls consist of the polyaddition product of a diisocyanate of the formula I

wherein

R denotes an alkylene radical having from 2 to 10 carbon atoms

and a diamine.

2. Use of microcapsules containing as core material a solution of a dye-precursor agent in a hydrophobic organic solvent, the walls of which microcapsules consist of the polyaddition product of a diisocyanate of the formula I

wherein

R denotes an alkylene radical having from 2 to 10 carbon atoms

and a diamine, for the production of pressure-sensitive copying papers.